Mersenne prime

Mersenne prime

Named after	Marin Mersenne
Publication year	1536
Author of publication	Regius, H.
No. of known terms	51
Conjectured no. of terms	Infinite
Subsequence of	Mersenne numbers
First terms	3, 7, 31, 127
Largest known term	282,589,933 − 1 (December 7, 2018)
OEIS index	A000668 Mersenne primes (of form 2^p - 1 where p is a prime)

In mathematics, a Mersenne prime is a prime number that is one less than a power of two. That is, it is a prime number of the form M_n = 2ⁿ − 1 for some integer n. They are named after Marin Mersenne, a French Minim friar, who studied them in the early 17th century.

The exponents n which give Mersenne primes are 2, 3, 5, 7, 13, 17, 19, 31, ... (sequence A000043 in the OEIS) and the resulting Mersenne primes are 3, 7, 31, 127, 8191, 131071, 524287, 2147483647, ... (sequence A000668 in the OEIS).

If n is a composite number then so is 2ⁿ − 1. (2^ab − 1 is divisible by both 2^a − 1 and 2^b − 1.) This definition is therefore equivalent to the definition as a prime number of the form M_p = 2^p − 1 for some prime p.

More generally, numbers of the form M_n = 2ⁿ − 1 without the primality requirement may be called Mersenne numbers. Sometimes, however, Mersenne numbers are defined to have the additional requirement that n be prime. The smallest composite Mersenne number with prime exponent n is 2¹¹ − 1 = 2047 = 23 × 89.

Mersenne primes M_p are also noteworthy due to their connection to perfect numbers.

As of June 2019, 51 Mersenne primes are known. The largest known prime number, 2^82,589,933 − 1, is a Mersenne prime. Since 1997, all newly found Mersenne primes have been discovered by the Great Internet Mersenne Prime Search (GIMPS), a distributed computing project on the Internet.

About Mersenne primes

Unsolved problem in mathematics:

Are there infinitely many Mersenne primes?

(more unsolved problems in mathematics)

Many fundamental questions about Mersenne primes remain unresolved. It is not even known whether the set of Mersenne primes is finite or infinite. The Lenstra–Pomerance–Wagstaff conjecture asserts that there are infinitely many Mersenne primes and predicts their order of growth. It is also not known whether infinitely many Mersenne numbers with prime exponents are composite, although this would follow from widely believed conjectures about prime numbers, for example, the infinitude of Sophie Germain primes congruent to 3 (mod 4). For these primes p, 2p + 1 (which is also prime) will divide M_p, for example, 23 | M₁₁, 47 | M₂₃, 167 | M₈₃, 263 | M₁₃₁, 359 | M₁₇₉, 383 | M₁₉₁, 479 | M₂₃₉, and 503 | M₂₅₁ (sequence A002515 in the OEIS). Since for these primes p, 2p + 1 is congruent to 7 mod 8, so 2 is a quadratic residue mod 2p + 1, and the multiplicative order of 2 mod 2p + 1 must divide ${\frac {(2p+1)-1}{2}}$ = p. Since p is a prime, it must be p or 1. However, it cannot be 1 since $\Phi _{1}(2)=1$ and 1 has no prime factors, so it must be p. Hence, 2p + 1 divides $\Phi _{p}(2)=2^{p}-1$ and $2^{p}-1=M_{p}$ cannot be prime.

The first four Mersenne primes are M₂ = 3, M₃ = 7, M₅ = 31 and M₇ = 127 and because the first Mersenne prime starts at M₂, all Mersenne primes are congruent to 3 (mod 4). Other than M₀ = 0 and M₁ = 1, all other Mersenne numbers are also congruent to 3 (mod 4). Consequently, in the prime factorization of a Mersenne number ( ≥ M₂ ) there must be at least one prime factor congruent to 3 (mod 4).

A basic theorem about Mersenne numbers states that if M_p is prime, then the exponent p must also be prime. This follows from the identity

${\begin{aligned}2^{ab}-1&=(2^{a}-1)\cdot \left(1+2^{a}+2^{2a}+2^{3a}+\cdots +2^{(b-1)a}\right)\\&=(2^{b}-1)\cdot \left(1+2^{b}+2^{2b}+2^{3b}+\cdots +2^{(a-1)b}\right).\end{aligned}}$

This rules out primality for Mersenne numbers with composite exponent, such as M₄ = 2⁴ − 1 = 15 = 3 × 5 = (2² − 1) × (1 + 2²).

Though the above examples might suggest that M_p is prime for all primes p, this is not the case, and the smallest counterexample is the Mersenne number

M₁₁ = 2¹¹ − 1 = 2047 = 23 × 89.

The evidence at hand suggests that a randomly selected Mersenne number is much more likely to be prime than an arbitrary randomly selected odd integer of similar size. Nonetheless, prime values of M_p appear to grow increasingly sparse as p increases. For example, eight of the first 11 primes p give rise to a Mersenne prime M_p (the correct terms on Mersenne's original list), while M_p is prime for only 43 of the first two million prime numbers (up to 32,452,843).

The lack of any simple test to determine whether a given Mersenne number is prime makes the search for Mersenne primes a difficult task, since Mersenne numbers grow very rapidly. The Lucas–Lehmer primality test (LLT) is an efficient primality test that greatly aids this task, making it much easier to test the primality of Mersenne numbers than that of most other numbers of the same size. The search for the largest known prime has somewhat of a cult following. Consequently, a lot of computer power has been expended searching for new Mersenne primes, much of which is now done using distributed computing.

Arithmetic modulo a Mersennne number is particularly efficient on a binary computer, making them popular choices when a prime modulus is desired, such as the Park–Miller random number generator. To find a primitive polynomial of Mersenne number order requires knowing the factorization of that number, so Mersenne primes allow one to find to primitive polynomials of very high order. Such primitive trinomials are used in pseudorandom number generators with very large periods such as the Mersenne twister, generalized shift register and Lagged Fibonacci generators.

Perfect numbers

Main article: Euclid–Euler theorem

Mersenne primes M_p are also noteworthy due to their connection with perfect numbers. In the 4th century BC, Euclid proved that if 2^p − 1 is prime, then 2^{p − 1}(2^p − 1) is a perfect number. This number, also expressible as M_p(M_p + 1)/2, is the M_pth triangular number and the 2^{p − 1}th hexagonal number. In the 18th century, Leonhard Euler proved that, conversely, all even perfect numbers have this form. This is known as the Euclid–Euler theorem. It is unknown whether there are any odd perfect numbers.

History

2	3	5	7	11	13	17	19
23	29	31	37	41	43	47	53
59	61	67	71	73	79	83	89
97	101	103	107	109	113	127	131
137	139	149	151	157	163	167	173
179	181	191	193	197	199	211	223
227	229	233	239	241	251	257	263
269	271	277	281	283	293	307	311
The first 64 prime exponents with those corresponding to Mersenne primes shaded in cyan and in bold, and those thought to do so by Mersenne in red and bold.

Mersenne primes take their name from the 17th-century French scholar Marin Mersenne, who compiled what was supposed to be a list of Mersenne primes with exponents up to 257. The exponents listed by Mersenne were as follows:

2, 3, 5, 7, 13, 17, 19, 31, 67, 127, 257.

His list replicated the known primes of his time with exponents up to 19. His next entry, 31, was correct, but the list then became largely incorrect, as Mersenne mistakenly included M₆₇ and M₂₅₇ (which are composite) and omitted M₆₁, M₈₉, and M₁₀₇ (which are prime). Mersenne gave little indication how he came up with his list.

Édouard Lucas proved in 1876 that M₁₂₇ is indeed prime, as Mersenne claimed. This was the largest known prime number for 75 years, and the largest ever found by hand. M₆₁ was determined to be prime in 1883 by Ivan Mikheevich Pervushin, though Mersenne claimed it was composite, and for this reason it is sometimes called Pervushin's number. This was the second-largest known prime number, and it remained so until 1911. Lucas had shown another error in Mersenne's list in 1876. Without finding a factor, Lucas demonstrated that M₆₇ is actually composite. No factor was found until a famous talk by Frank Nelson Cole in 1903. Without speaking a word, he went to a blackboard and raised 2 to the 67th power, then subtracted one. On the other side of the board, he multiplied 193,707,721 × 761,838,257,287 and got the same number, then returned to his seat (to applause) without speaking. He later said that the result had taken him "three years of Sundays" to find. A correct list of all Mersenne primes in this number range was completed and rigorously verified only about three centuries after Mersenne published his list.

Searching for Mersenne primes

Fast algorithms for finding Mersenne primes are available, and as of June 2019 the seven largest known prime numbers are Mersenne primes.

The first four Mersenne primes M₂ = 3, M₃ = 7, M₅ = 31 and M₇ = 127 were known in antiquity. The fifth, M₁₃ = 8191, was discovered anonymously before 1461; the next two (M₁₇ and M₁₉) were found by Pietro Cataldi in 1588. After nearly two centuries, M₃₁ was verified to be prime by Leonhard Euler in 1772. The next (in historical, not numerical order) was M₁₂₇, found by Édouard Lucas in 1876, then M₆₁ by Ivan Mikheevich Pervushin in 1883. Two more (M₈₉ and M₁₀₇) were found early in the 20th century, by R. E. Powers in 1911 and 1914, respectively.

The best method presently known for testing the primality of Mersenne numbers is the Lucas–Lehmer primality test. Specifically, it can be shown that for prime p > 2, M_p = 2^p − 1 is prime if and only if M_p divides S_{p − 2}, where S₀ = 4 and S_k = (S_{k − 1})² − 2 for k > 0.

During the era of manual calculation, all the exponents up to and including 257 were tested with the Lucas–Lehmer test and found to be composite. A notable contribution was made by retired Yale physics professor Horace Scudder Uhler, who did the calculations for exponents 157, 167, 193, 199, 227, and 229. Unfortunately for those investigators, the interval they were testing contains the largest known relative gap between Mersenne primes; in relative terms: the next Mersenne prime exponent, 521, would turn out to be more than four times larger than the previous record of 127.

Graph of number of digits in largest known Mersenne prime by year – electronic era. Note that the vertical scale, the number of digits, is doubly logarithmic in the value of the prime.

The search for Mersenne primes was revolutionized by the introduction of the electronic digital computer. Alan Turing searched for them on the Manchester Mark 1 in 1949, but the first successful identification of a Mersenne prime, M₅₂₁, by this means was achieved at 10:00 pm on January 30, 1952 using the U.S. National Bureau of Standards Western Automatic Computer (SWAC) at the Institute for Numerical Analysis at the University of California, Los Angeles, under the direction of Lehmer, with a computer search program written and run by Prof. R. M. Robinson. It was the first Mersenne prime to be identified in thirty-eight years; the next one, M₆₀₇, was found by the computer a little less than two hours later. Three more — M₁₂₇₉, M₂₂₀₃, M₂₂₈₁ — were found by the same program in the next several months. M₄₂₅₃ is the first Mersenne prime that is titanic, M_44,497 is the first gigantic, and M_6,972,593 was the first megaprime to be discovered, being a prime with at least 1,000,000 digits. All three were the first known prime of any kind of that size. The number of digits in the decimal representation of M_n equals ⌊n × log₁₀2⌋ + 1, where ⌊x⌋ denotes the floor function (or equivalently ⌊log₁₀M_n⌋ + 1).

In September 2008, mathematicians at UCLA participating in GIMPS won part of a $100,000 prize from the Electronic Frontier Foundation for their discovery of a very nearly 13-million-digit Mersenne prime. The prize, finally confirmed in October 2009, is for the first known prime with at least 10 million digits. The prime was found on a Dell OptiPlex 745 on August 23, 2008. This was the eighth Mersenne prime discovered at UCLA.

On April 12, 2009, a GIMPS server log reported that a 47th Mersenne prime had possibly been found. The find was first noticed on June 4, 2009, and verified a week later. The prime is 2^42,643,801 − 1. Although it is chronologically the 47th Mersenne prime to be discovered, it is smaller than the largest known at the time, which was the 45th to be discovered.

On January 25, 2013, Curtis Cooper, a mathematician at the University of Central Missouri, discovered a 48th Mersenne prime, 2^57,885,161 − 1 (a number with 17,425,170 digits), as a result of a search executed by a GIMPS server network.

On January 19, 2016, Cooper published his discovery of a 49th Mersenne prime, 2^74,207,281 − 1 (a number with 22,338,618 digits), as a result of a search executed by a GIMPS server network. This was the fourth Mersenne prime discovered by Cooper and his team in the past ten years.

On September 2, 2016, the Great Internet Mersenne Prime Search finished verifying all tests below M_37,156,667, thus officially confirming its position as the 45th Mersenne prime.

On January 3, 2018, it was announced that Jonathan Pace, a 51-year-old electrical engineer living in Germantown, Tennessee, had found a 50th Mersenne prime, 2^77,232,917 − 1 (a number with 23,249,425 digits), as a result of a search executed by a GIMPS server network.

On December 21, 2018, it was announced that The Great Internet Mersenne Prime Search (GIMPS) discovered the largest known prime number, 2^82,589,933 − 1, having 24,862,048 digits. A computer volunteered by Patrick Laroche from Ocala, Florida made the find on December 7, 2018.

Theorems about Mersenne numbers

1. If a and p are natural numbers such that a^p − 1 is prime, then a = 2 or p = 1.
   • Proof: a ≡ 1 (mod a − 1). Then a^p ≡ 1 (mod a − 1), so a^p − 1 ≡ 0 (mod a − 1). Thus a − 1 | a^p − 1. However, a^p − 1 is prime, so a − 1 = a^p − 1 or a − 1 = ±1. In the former case, a = a^p, hence a = 0,1 (which is a contradiction, as neither −1 nor 0 is prime) or p = 1. In the latter case, a = 2 or a = 0. If a = 0, however, 0^p − 1 = 0 − 1 = −1 which is not prime. Therefore, a = 2.
2. If 2^p − 1 is prime, then p is prime.
   • Proof: suppose that p is composite, hence can be written p = ab with a and b > 1. Then 2^p − 1 = 2^ab − 1 = (2^a)^b − 1 = (2^a − 1)((2^a)^b−1 + (2^a)^b−2 + … + 2^a + 1) so 2^p − 1 is composite. By contrapositive, if 2^p − 1 is prime then p is prime.
3. If p is an odd prime, then every prime q that divides 2^p − 1 must be 1 plus a multiple of 2p. This holds even when 2^p − 1 is prime.
   • For example, 2⁵ − 1 = 31 is prime, and 31 = 1 + 3 × (2 × 5). A composite example is 2¹¹ − 1 = 23 × 89, where 23 = 1 + (2 × 11) and 89 = 1 + 4 × (2 × 11).
   • Proof: By Fermat's little theorem, q is a factor of 2^q−1 − 1. Since q is a factor of 2^p − 1, for all positive integers c, q is also a factor of 2^pc − 1. Since p is prime and q is not a factor of 2¹ − 1, p is also the smallest positive integer x such that q is a factor of 2^x − 1. As a result, for all positive integers x, q is a factor of 2^x − 1 if and only if p is a factor of x. Therefore, since q is a factor of 2^q−1 − 1, p is a factor of q − 1 so q ≡ 1 (mod p). Furthermore, since q is a factor of 2^p − 1, which is odd, q is odd. Therefore, q ≡ 1 (mod 2p).
   • This fact leads to a proof of Euclid's theorem, which asserts the infinitude of primes, distinct from the proof written by Euclid: for every odd prime p, all primes dividing 2^p − 1 are larger than p; thus there are always larger primes than any particular prime.
   • It follows from this fact that for every prime p > 2, there is at least one prime of the form 2kp+1 less than or equal to M_p, for some integer k.
4. If p is an odd prime, then every prime q that divides 2^p − 1 is congruent to ±1 (mod 8).
   • Proof: 2^p+1 ≡ 2 (mod q), so 2^1/2(p+1) is a square root of 2 mod q. By quadratic reciprocity, every prime modulus in which the number 2 has a square root is congruent to ±1 (mod 8).
5. A Mersenne prime cannot be a Wieferich prime.
   • Proof: We show if p = 2^m − 1 is a Mersenne prime, then the congruence 2^p−1 ≡ 1 (mod p²) does not hold. By Fermat's little theorem, m | p − 1. Therefore, one can write p − 1 = mλ. If the given congruence is satisfied, then p² | 2^mλ − 1, therefore 0 ≡ 2^mλ − 1/2^m − 1 = 1 + 2^m + 2^2m + ... + 2^{(λ − 1)m} ≡ −λ mod (2^m − 1). Hence 2^m − 1 | λ, and therefore λ ≥ 2^m − 1. This leads to p − 1 ≥ m(2^m − 1), which is impossible since m ≥ 2.
6. If m and n are natural numbers then m and n are coprime if and only if 2^m − 1 and 2ⁿ − 1 are coprime. Consequently, a prime number divides at most one prime-exponent Mersenne number, so in other words the set of pernicious Mersenne numbers is pairwise coprime.
7. If p and 2p + 1 are both prime (meaning that p is a Sophie Germain prime), and p is congruent to 3 (mod 4), then 2p + 1 divides 2^p − 1.
   • Example: 11 and 23 are both prime, and 11 = 2 × 4 + 3, so 23 divides 2¹¹ − 1.
   • Proof: Let q be 2p + 1. By Fermat's little theorem, 2^2p ≡ 1 (mod q), so either 2^p ≡ 1 (mod q) or 2^p ≡ −1 (mod q). Supposing latter true, then 2^p+1 = (2^{1/2(p + 1)})² ≡ −2 (mod q), so −2 would be a quadratic residue mod q. However, since p is congruent to 3 (mod 4), q is congruent to 7 (mod 8) and therefore 2 is a quadratic residue mod q. Also since q is congruent to 3 (mod 4), −1 is a quadratic nonresidue mod q, so −2 is the product of a residue and a nonresidue and hence it is a nonresidue, which is a contradiction. Hence, the former congruence must be true and 2p + 1 divides M_p.
8. All composite divisors of prime-exponent Mersenne numbers are strong pseudoprimes to the base 2.
9. With the exception of 1, a Mersenne number cannot be a perfect power. In other words, and in accordance with Mihăilescu's theorem, the equation 2^m − 1 = n^k has no solutions where m, n, and k are integers with m > 1 and k > 1.

List of known Mersenne primes

The table below lists all known Mersenne primes (sequence A000043 (p) and A000668 (M_p) in OEIS):

#	p	Mp	Mp digits	Discovered	Discoverer	Method used
1	2	3	1	c. 430 BC	Ancient Greek mathematicians
2	3	7	1	c. 430 BC	Ancient Greek mathematicians
3	5	31	2	c. 300 BC	Ancient Greek mathematicians
4	7	127	3	c. 300 BC	Ancient Greek mathematicians
5	13	8191	4	1456	Anonymous	Trial division
6	17	131071	6	1588	Pietro Cataldi	Trial division
7	19	524287	6	1588	Pietro Cataldi	Trial division
8	31	2147483647	10	1772	Leonhard Euler	Trial division with modular restrictions
9	61	2305843009213693951	19	1883 November	Ivan M. Pervushin	Lucas sequences
10	89	618970019642...137449562111	27	1911 June	Ralph Ernest Powers	Lucas sequences
11	107	162259276829...578010288127	33	1914 June 1	Ralph Ernest Powers	Lucas sequences
12	127	170141183460...715884105727	39	1876 January 10	Édouard Lucas	Lucas sequences
13	521	686479766013...291115057151	157	1952 January 30	Raphael M. Robinson	LLT / SWAC
14	607	531137992816...219031728127	183	1952 January 30	Raphael M. Robinson	LLT / SWAC
15	1,279	104079321946...703168729087	386	1952 June 25	Raphael M. Robinson	LLT / SWAC
16	2,203	147597991521...686697771007	664	1952 October 7	Raphael M. Robinson	LLT / SWAC
17	2,281	446087557183...418132836351	687	1952 October 9	Raphael M. Robinson	LLT / SWAC
18	3,217	259117086013...362909315071	969	1957 September 8	Hans Riesel	LLT / BESK
19	4,253	190797007524...815350484991	1,281	1961 November 3	Alexander Hurwitz	LLT / IBM 7090
20	4,423	285542542228...902608580607	1,332	1961 November 3	Alexander Hurwitz	LLT / IBM 7090
21	9,689	478220278805...826225754111	2,917	1963 May 11	Donald B. Gillies	LLT / ILLIAC II
22	9,941	346088282490...883789463551	2,993	1963 May 16	Donald B. Gillies	LLT / ILLIAC II
23	11,213	281411201369...087696392191	3,376	1963 June 2	Donald B. Gillies	LLT / ILLIAC II
24	19,937	431542479738...030968041471	6,002	1971 March 4	Bryant Tuckerman	LLT / IBM 360/91
25	21,701	448679166119...353511882751	6,533	1978 October 30	Landon Curt Noll & Laura Nickel	LLT / CDC Cyber 174
26	23,209	402874115778...523779264511	6,987	1979 February 9	Landon Curt Noll	LLT / CDC Cyber 174
27	44,497	854509824303...961011228671	13,395	1979 April 8	Harry L. Nelson & David Slowinski	LLT / Cray 1
28	86,243	536927995502...709433438207	25,962	1982 September 25	David Slowinski	LLT / Cray 1
29	110,503	521928313341...083465515007	33,265	1988 January 29	Walter Colquitt & Luke Welsh	LLT / NEC SX-2
30	132,049	512740276269...455730061311	39,751	1983 September 19	David Slowinski	LLT / Cray X-MP
31	216,091	746093103064...103815528447	65,050	1985 September 1	David Slowinski	LLT / Cray X-MP/24
32	756,839	174135906820...328544677887	227,832	1992 February 17	David Slowinski & Paul Gage	LLT / Harwell Lab's Cray-2
33	859,433	129498125604...243500142591	258,716	1994 January 4	David Slowinski & Paul Gage	LLT / Cray C90
34	1,257,787	412245773621...976089366527	378,632	1996 September 3	David Slowinski & Paul Gage	LLT / Cray T94
35	1,398,269	814717564412...868451315711	420,921	1996 November 13	GIMPS / Joel Armengaud	LLT / Prime95 on 90 MHz Pentium
36	2,976,221	623340076248...743729201151	895,932	1997 August 24	GIMPS / Gordon Spence	LLT / Prime95 on 100 MHz Pentium
37	3,021,377	127411683030...973024694271	909,526	1998 January 27	GIMPS / Roland Clarkson	LLT / Prime95 on 200 MHz Pentium
38	6,972,593	437075744127...142924193791	2,098,960	1999 June 1	GIMPS / Nayan Hajratwala	LLT / Prime95 on 350 MHz Pentium II IBM Aptiva
39	13,466,917	924947738006...470256259071	4,053,946	2001 November 14	GIMPS / Michael Cameron	LLT / Prime95 on 800 MHz Athlon T-Bird
40	20,996,011	125976895450...762855682047	6,320,430	2003 November 17	GIMPS / Michael Shafer	LLT / Prime95 on 2 GHz Dell Dimension
41	24,036,583	299410429404...882733969407	7,235,733	2004 May 15	GIMPS / Josh Findley	LLT / Prime95 on 2.4 GHz Pentium 4
42	25,964,951	122164630061...280577077247	7,816,230	2005 February 18	GIMPS / Martin Nowak	LLT / Prime95 on 2.4 GHz Pentium 4
43	30,402,457	315416475618...411652943871	9,152,052	2005 December 15	GIMPS / Curtis Cooper & Steven Boone	LLT / Prime95 on 2 GHz Pentium 4
44	32,582,657	124575026015...154053967871	9,808,358	2006 September 4	GIMPS / Curtis Cooper & Steven Boone	LLT / Prime95 on 3 GHz Pentium 4
45	37,156,667	202254406890...022308220927	11,185,272	2008 September 6	GIMPS / Hans-Michael Elvenich	LLT / Prime95 on 2.83 GHz Core 2 Duo
46	42,643,801	169873516452...765562314751	12,837,064	2009 June 4	GIMPS / Odd M. Strindmo	LLT / Prime95 on 3 GHz Core 2
47	43,112,609	316470269330...166697152511	12,978,189	2008 August 23	GIMPS / Edson Smith	LLT / Prime95 on Dell Optiplex 745
48	57,885,161	581887266232...071724285951	17,425,170	2013 January 25	GIMPS / Curtis Cooper	LLT / Prime95 on 3 GHz Intel Core2 Duo E8400
49	74,207,281	300376418084...391086436351	22,338,618	2016 January 7	GIMPS / Curtis Cooper	LLT / Prime95 on Intel Core i7-4790
50	77,232,917	467333183359...069762179071	23,249,425	2017 December 26	GIMPS / Jon Pace	LLT / Prime95 on 3.3 GHz Intel Core i5-6600
51	82,589,933	148894445742...325217902591	24,862,048	2018 December 7	GIMPS / Patrick Laroche	LLT / Prime95 on Intel Core i5-4590T

All Mersenne numbers below the 51st Mersenne prime (M_82,589,933) have been tested at least once but some have not been double-checked. Primes are not always discovered in increasing order. For example, the 29th Mersenne prime was discovered after the 30th and the 31st. Similarly, M_43,112,609 was followed by two smaller Mersenne primes, first 2 weeks later and then 9 months later. M_43,112,609 was the first discovered prime number with more than 10 million decimal digits.

The largest known Mersenne prime (2^82,589,933 − 1) is also the largest known prime number.

The largest known prime has been a Mersenne prime since 1952, except between 1989 and 1992.

Factorization of composite Mersenne numbers

Since they are prime numbers, Mersenne primes are divisible only by 1 and by themselves. However, not all Mersenne numbers are Mersenne primes, and the composite Mersenne numbers may be factored non-trivially. Mersenne numbers are very good test cases for the special number field sieve algorithm, so often the largest number factorized with this algorithm has been a Mersenne number. As of June 2019, 2^1,193 − 1 is the record-holder, having been factored with a variant of the special number field sieve that allows the factorization of several numbers at once. See integer factorization records for links to more information. The special number field sieve can factorize numbers with more than one large factor. If a number has only one very large factor then other algorithms can factorize larger numbers by first finding small factors and then making a primality test on the cofactor. As of June 2019, the largest factorization with probable prime factors allowed is 2^7,313,983 − 1 = 305,492,080,276,193 × q, where q is a 2,201,714-digit probable prime. It was discovered by Oliver Kruse. As of June 2019, the Mersenne number M₁₂₇₇ is the smallest composite Mersenne number with no known factors; it has no prime factors below 2⁶⁷.

The table below shows factorizations for the first 20 composite Mersenne numbers (sequence A244453 in the OEIS).

p	Mp	Factorization of Mp
11	2047	23 × 89
23	8388607	47 × 178,481
29	536870911	233 × 1,103 × 2,089
37	137438953471	223 × 616,318,177
41	2199023255551	13,367 × 164,511,353
43	8796093022207	431 × 9,719 × 2,099,863
47	140737488355327	2,351 × 4,513 × 13,264,529
53	9007199254740991	6,361 × 69,431 × 20,394,401
59	57646075230343487	179,951 × 3,203,431,780,337 (13 digits)
67	147573952589676412927	193,707,721 × 761,838,257,287 (12 digits)
71	2361183241434822606847	228,479 × 48,544,121 × 212,885,833
73	9444732965739290427391	439 × 2,298,041 × 9,361,973,132,609 (13 digits)
79	604462903807314587353087	2,687 × 202,029,703 × 1,113,491,139,767 (13 digits)
83	967140655691...033397649407	167 × 57,912,614,113,275,649,087,721 (23 digits)
97	158456325028...187087900671	11,447 × 13,842,607,235,828,485,645,766,393 (26 digits)
101	253530120045...993406410751	7,432,339,208,719 (13 digits) × 341,117,531,003,194,129 (18 digits)
103	101412048018...973625643007	2,550,183,799 × 3,976,656,429,941,438,590,393 (22 digits)
109	649037107316...312041152511	745,988,807 × 870,035,986,098,720,987,332,873 (24 digits)
113	103845937170...992658440191	3,391 × 23,279 × 65,993 × 1,868,569 × 1,066,818,132,868,207 (16 digits)
131	272225893536...454145691647	263 × 10,350,794,431,055,162,386,718,619,237,468,234,569 (38 digits)

The number of factors for the first 500 Mersenne numbers can be found at (sequence A046800 in the OEIS).

Mersenne numbers in nature and elsewhere

In the mathematical problem Tower of Hanoi, solving a puzzle with an n-disc tower requires M_n steps, assuming no mistakes are made. The number of rice grains on the whole chessboard in the wheat and chessboard problem is M₆₄.

The asteroid with minor planet number 8191 is named 8191 Mersenne after Marin Mersenne, because 8191 is a Mersenne prime (3 Juno, 7 Iris, 31 Euphrosyne and 127 Johanna having been discovered and named during the 19th century).

In geometry, an integer right triangle that is primitive and has its even leg a power of 2 ( ≥ 4 ) generates a unique right triangle such that its inradius is always a Mersenne number. For example, if the even leg is 2^n + 1 then because it is primitive it constrains the odd leg to be 4ⁿ − 1, the hypotenuse to be 4ⁿ + 1 and its inradius to be 2ⁿ − 1.

The Mersenne numbers were studied with respect to the total number of accepting paths of non-deterministic polynomial time Turing machines in 2018 and intriguing inclusions were discovered.

Mersenne–Fermat primes

A Mersenne–Fermat number is defined as 2^pr − 1/2^{pr − 1} − 1, with p prime, r natural number, and can be written as MF(p, r), when r = 1, it is a Mersenne number, and when p = 2, it is a Fermat number, the only known Mersenne–Fermat prime with r > 1 are

MF(2, 2), MF(3, 2), MF(7, 2), MF(59, 2), MF(2, 3), MF(3, 3), MF(2, 4), and MF(2, 5).

In fact, MF(p, r) = Φ_p^r(2), where Φ is the cyclotomic polynomial.

Generalizations

The simplest generalized Mersenne primes are prime numbers of the form f(2ⁿ), where f(x) is a low-degree polynomial with small integer coefficients. An example is 2⁶⁴ − 2³² + 1, in this case, n = 32, and f(x) = x² − x + 1; another example is 2¹⁹² − 2⁶⁴ − 1, in this case, n = 64, and f(x) = x³ − x − 1.

It is also natural to try to generalize primes of the form 2ⁿ − 1 to primes of the form bⁿ − 1 (for b ≠ 2 and n > 1). However (see also theorems above), bⁿ − 1 is always divisible by b − 1, so unless the latter is a unit, the former is not a prime. This can be remedied by allowing b to be an algebraic integer instead of an integer:

Complex numbers

In the ring of integers (on real numbers), if b − 1 is a unit, then b is either 2 or 0. But 2ⁿ − 1 are the usual Mersenne primes, and the formula 0ⁿ − 1 does not lead to anything interesting (since it is always −1 for all n > 0). Thus, we can regard a ring of "integers" on complex numbers instead of real numbers, like Gaussian integers and Eisenstein integers.

Gaussian Mersenne primes

If we regard the ring of Gaussian integers, we get the case b = 1 + i and b = 1 − i, and can ask (WLOG) for which n the number (1 + i)ⁿ − 1 is a Gaussian prime which will then be called a Gaussian Mersenne prime.

(1 + i)ⁿ − 1 is a Gaussian prime for the following n:

2, 3, 5, 7, 11, 19, 29, 47, 73, 79, 113, 151, 157, 163, 167, 239, 241, 283, 353, 367, 379, 457, 997, 1367, 3041, 10141, 14699, 27529, 49207, 77291, 85237, 106693, 160423, 203789, 364289, 991961, 1203793, 1667321, 3704053, 4792057, ... (sequence A057429 in the OEIS)

Like the sequence of exponents for usual Mersenne primes, this sequence contains only (rational) prime numbers.

As for all Gaussian primes, the norms (that is, squares of absolute values) of these numbers are rational primes:

5, 13, 41, 113, 2113, 525313, 536903681, 140737471578113, ... (sequence A182300 in the OEIS).

Eisenstein Mersenne primes

We can also regard the ring of Eisenstein integers, we get the case b = 1 + ω and b = 1 − ω, and can ask for what n the number (1 + ω)ⁿ − 1 is an Eisenstein prime which will then be called a Eisenstein Mersenne prime.

(1 + ω)ⁿ − 1 is an Eisenstein prime for the following n:

2, 5, 7, 11, 17, 19, 79, 163, 193, 239, 317, 353, 659, 709, 1049, 1103, 1759, 2029, 5153, 7541, 9049, 10453, 23743, 255361, 534827, 2237561, ... (sequence A066408 in the OEIS)

The norms (that is, squares of absolute values) of these Eisenstein primes are rational primes:

7, 271, 2269, 176419, 129159847, 1162320517, ... (sequence A066413 in the OEIS)

Divide an integer

Repunit primes

Main article: Repunit

The other way to deal with the fact that bⁿ − 1 is always divisible by b − 1, it is to simply take out this factor and ask which values of n make

${\frac {b^{n}-1}{b-1}}$

be prime. (The integer b can be either positive or negative.) If, for example, we take b = 10, we get n values of:

2, 19, 23, 317, 1031, 49081, 86453, 109297, 270343, ... (sequence A004023 in the OEIS),
corresponding to primes 11, 1111111111111111111, 11111111111111111111111, ... (sequence A004022 in the OEIS).

These primes are called repunit primes. Another example is when we take b = −12, we get n values of:

2, 5, 11, 109, 193, 1483, 11353, 21419, 21911, 24071, 106859, 139739, ... (sequence A057178 in the OEIS),
corresponding to primes −11, 19141, 57154490053, ....

It is a conjecture that for every integer b which is not a perfect power, there are infinitely many values of n such that bⁿ − 1/b − 1 is prime. (When b is a perfect power, it can be shown that there is at most one n value such that bⁿ − 1/b − 1 is prime)

Least n such that bⁿ − 1/b − 1 is prime are (starting with b = 2, 0 if no such n exists)

2, 3, 2, 3, 2, 5, 3, 0, 2, 17, 2, 5, 3, 3, 2, 3, 2, 19, 3, 3, 2, 5, 3, 0, 7, 3, 2, 5, 2, 7, 0, 3, 13, 313, 2, 13, 3, 349, 2, 3, 2, 5, 5, 19, 2, 127, 19, 0, 3, 4229, 2, 11, 3, 17, 7, 3, 2, 3, 2, 7, 3, 5, 0, 19, 2, 19, 5, 3, 2, 3, 2, ... (sequence A084740 in the OEIS)

For negative bases b, they are (starting with b = −2, 0 if no such n exists)

3, 2, 2, 5, 2, 3, 2, 3, 5, 5, 2, 3, 2, 3, 3, 7, 2, 17, 2, 3, 3, 11, 2, 3, 11, 0, 3, 7, 2, 109, 2, 5, 3, 11, 31, 5, 2, 3, 53, 17, 2, 5, 2, 103, 7, 5, 2, 7, 1153, 3, 7, 21943, 2, 3, 37, 53, 3, 17, 2, 7, 2, 3, 0, 19, 7, 3, 2, 11, 3, 5, 2, ... (sequence A084742 in the OEIS) (notice this OEIS sequence does not allow n = 2)

Least base b such that b^prime(n) − 1/b − 1 is prime are

2, 2, 2, 2, 5, 2, 2, 2, 10, 6, 2, 61, 14, 15, 5, 24, 19, 2, 46, 3, 11, 22, 41, 2, 12, 22, 3, 2, 12, 86, 2, 7, 13, 11, 5, 29, 56, 30, 44, 60, 304, 5, 74, 118, 33, 156, 46, 183, 72, 606, 602, 223, 115, 37, 52, 104, 41, 6, 338, 217, ... (sequence A066180 in the OEIS)

For negative bases b, they are

3, 2, 2, 2, 2, 2, 2, 2, 2, 7, 2, 16, 61, 2, 6, 10, 6, 2, 5, 46, 18, 2, 49, 16, 70, 2, 5, 6, 12, 92, 2, 48, 89, 30, 16, 147, 19, 19, 2, 16, 11, 289, 2, 12, 52, 2, 66, 9, 22, 5, 489, 69, 137, 16, 36, 96, 76, 117, 26, 3, ... (sequence A103795 in the OEIS)

Other generalized Mersenne primes

Another generalized Mersenne number is

${\frac {a^{n}-b^{n}}{a-b}}$

with a, b any coprime integers, a > 1 and −a < b < a. (Since aⁿ − bⁿ is always divisible by a − b, the division is necessary for there to be any chance of finding prime numbers. In fact, this number is the same as the Lucas number U_n(a + b, ab), since a and b are the roots of the quadratic equation x² − (a + b)x + ab = 0, and this number equals 1 when n = 1) We can ask which n makes this number prime. It can be shown that such n must be primes themselves or equal to 4, and n can be 4 if and only if a + b = 1 and a² + b² is prime. (Since a⁴ − b⁴/a − b = (a + b)(a² + b²). Thus, in this case the pair (a, b) must be (x + 1, −x) and x² + (x + 1)² must be prime. That is, x must be in OEIS: A027861.) It is a conjecture that for any pair (a, b) such that for every natural number r > 1, a and b are not both perfect rth powers, and −4ab is not a perfect fourth power. there are infinitely many values of n such that aⁿ − bⁿ/a − b is prime. (When a and b are both perfect rth powers for an r > 1 or when −4ab is a perfect fourth power, it can be shown that there are at most two n values with this property, since if so, then aⁿ − bⁿ/a − b can be factored algebraically) However, this has not been proved for any single value of (a, b).

For more information, see

a	b	numbers n such that an − bn/a − b is prime (some large terms are only probable primes, these n are checked up to 100000 for |b| ≤ 5 or |b| = a − 1, 20000 for 5 < |b| < a − 1)	OEIS sequence
2	1	2, 3, 5, 7, 13, 17, 19, 31, 61, 89, 107, 127, 521, 607, 1279, 2203, 2281, 3217, 4253, 4423, 9689, 9941, 11213, 19937, 21701, 23209, 44497, 86243, 110503, 132049, 216091, 756839, 859433, 1257787, 1398269, 2976221, 3021377, 6972593, 13466917, 20996011, 24036583, 25964951, 30402457, 32582657, 37156667, 42643801, 43112609, ..., 57885161, ..., 74207281, ..., 77232917, ..., 82589933, ...	A000043
2	−1	3, 4*, 5, 7, 11, 13, 17, 19, 23, 31, 43, 61, 79, 101, 127, 167, 191, 199, 313, 347, 701, 1709, 2617, 3539, 5807, 10501, 10691, 11279, 12391, 14479, 42737, 83339, 95369, 117239, 127031, 138937, 141079, 267017, 269987, 374321, 986191, 4031399, ..., 13347311, 13372531, ...	A000978
3	2	2, 3, 5, 17, 29, 31, 53, 59, 101, 277, 647, 1061, 2381, 2833, 3613, 3853, 3929, 5297, 7417, 90217, 122219, 173191, 256199, 336353, 485977, 591827, 1059503, ...	A057468
3	1	3, 7, 13, 71, 103, 541, 1091, 1367, 1627, 4177, 9011, 9551, 36913, 43063, 49681, 57917, 483611, 877843, ...	A028491
3	−1	2*, 3, 5, 7, 13, 23, 43, 281, 359, 487, 577, 1579, 1663, 1741, 3191, 9209, 11257, 12743, 13093, 17027, 26633, 104243, 134227, 152287, 700897, 1205459, ...	A007658
3	−2	3, 4*, 7, 11, 83, 149, 223, 599, 647, 1373, 8423, 149497, 388897, ...	A057469
4	3	2, 3, 7, 17, 59, 283, 311, 383, 499, 521, 541, 599, 1193, 1993, 2671, 7547, 24019, 46301, 48121, 68597, 91283, 131497, 148663, 184463, 341233, ...	A059801
4	1	2 (no others)
4	−1	2*, 3 (no others)
4	−3	3, 5, 19, 37, 173, 211, 227, 619, 977, 1237, 2437, 5741, 13463, 23929, 81223, 121271, ...	A128066
5	4	3, 43, 59, 191, 223, 349, 563, 709, 743, 1663, 5471, 17707, 19609, 35449, 36697, 45259, 91493, 246497, 265007, 289937, ...	A059802
5	3	13, 19, 23, 31, 47, 127, 223, 281, 2083, 5281, 7411, 7433, 19051, 27239, 35863, 70327, ...	A121877
5	2	2, 5, 7, 13, 19, 37, 59, 67, 79, 307, 331, 599, 1301, 12263, 12589, 18443, 20149, 27983, ...	A082182
5	1	3, 7, 11, 13, 47, 127, 149, 181, 619, 929, 3407, 10949, 13241, 13873, 16519, 201359, 396413, 1888279, ...	A004061
5	−1	5, 67, 101, 103, 229, 347, 4013, 23297, 30133, 177337, 193939, 266863, 277183, 335429, ...	A057171
5	−2	2*, 3, 17, 19, 47, 101, 1709, 2539, 5591, 6037, 8011, 19373, 26489, 27427, ...	A082387
5	−3	2*, 3, 5, 7, 17, 19, 109, 509, 661, 709, 1231, 12889, 13043, 26723, 43963, 44789, ...	A122853
5	−4	4*, 5, 7, 19, 29, 61, 137, 883, 1381, 1823, 5227, 25561, 29537, 300893, ...	A128335
6	5	2, 5, 11, 13, 23, 61, 83, 421, 1039, 1511, 31237, 60413, 113177, 135647, 258413, ...	A062572
6	1	2, 3, 7, 29, 71, 127, 271, 509, 1049, 6389, 6883, 10613, 19889, 79987, 608099, ...	A004062
6	−1	2*, 3, 11, 31, 43, 47, 59, 107, 811, 2819, 4817, 9601, 33581, 38447, 41341, 131891, 196337, ...	A057172
6	−5	3, 4*, 5, 17, 397, 409, 643, 1783, 2617, 4583, 8783, ...	A128336
7	6	2, 3, 7, 29, 41, 67, 1327, 1399, 2027, 69371, 86689, 355039, ...	A062573
7	5	3, 5, 7, 113, 397, 577, 7573, 14561, 58543, ...	A128344
7	4	2, 5, 11, 61, 619, 2879, 2957, 24371, 69247, ...	A213073
7	3	3, 7, 19, 109, 131, 607, 863, 2917, 5923, 12421, ...	A128024
7	2	3, 7, 19, 79, 431, 1373, 1801, 2897, 46997, ...	A215487
7	1	5, 13, 131, 149, 1699, 14221, 35201, 126037, 371669, 1264699, ...	A004063
7	−1	3, 17, 23, 29, 47, 61, 1619, 18251, 106187, 201653, ...	A057173
7	−2	2*, 5, 23, 73, 101, 401, 419, 457, 811, 1163, 1511, 8011, ...	A125955
7	−3	3, 13, 31, 313, 3709, 7933, 14797, 30689, 38333, ...	A128067
7	−4	2*, 3, 5, 19, 41, 47, 8231, 33931, 43781, 50833, 53719, 67211, ...	A218373
7	−5	2*, 11, 31, 173, 271, 547, 1823, 2111, 5519, 7793, 22963, 41077, 49739, ...	A128337
7	−6	3, 53, 83, 487, 743, ...	A187805
8	7	7, 11, 17, 29, 31, 79, 113, 131, 139, 4357, 44029, 76213, 83663, 173687, 336419, 615997, ...	A062574
8	5	2, 19, 1021, 5077, 34031, 46099, 65707, ...	A128345
8	3	2, 3, 7, 19, 31, 67, 89, 9227, 43891, ...	A128025
8	1	3 (no others)
8	−1	2* (no others)
8	−3	2*, 5, 163, 191, 229, 271, 733, 21059, 25237, ...	A128068
8	−5	2*, 7, 19, 167, 173, 223, 281, 21647, ...	A128338
8	−7	4*, 7, 13, 31, 43, 269, 353, 383, 619, 829, 877, 4957, 5711, 8317, 21739, 24029, 38299, ...	A181141
9	8	2, 7, 29, 31, 67, 149, 401, 2531, 19913, 30773, 53857, 170099, ...	A059803
9	7	3, 5, 7, 4703, 30113, ...	A273010
9	5	3, 11, 17, 173, 839, 971, 40867, 45821, ...	A128346
9	4	2 (no others)
9	2	2, 3, 5, 13, 29, 37, 1021, 1399, 2137, 4493, 5521, ...	A173718
9	1	(none)
9	−1	3, 59, 223, 547, 773, 1009, 1823, 3803, 49223, 193247, 703393, ...	A057175
9	−2	2*, 3, 7, 127, 283, 883, 1523, 4001, ...	A125956
9	−4	2*, 3, 5, 7, 11, 17, 19, 41, 53, 109, 167, 2207, 3623, 5059, 5471, 7949, 21211, 32993, 60251, ...	A211409
9	−5	3, 5, 13, 17, 43, 127, 229, 277, 6043, 11131, 11821, ...	A128339
9	−7	2*, 3, 107, 197, 2843, 3571, 4451, ..., 31517, ...	A301369
9	−8	3, 7, 13, 19, 307, 619, 2089, 7297, 75571, 76103, 98897, ...	A187819
10	9	2, 3, 7, 11, 19, 29, 401, 709, 2531, 15787, 66949, 282493, ...	A062576
10	7	2, 31, 103, 617, 10253, 10691, ...	A273403
10	3	2, 3, 5, 37, 599, 38393, 51431, ...	A128026
10	1	2, 19, 23, 317, 1031, 49081, 86453, 109297, 270343, ...	A004023
10	−1	5, 7, 19, 31, 53, 67, 293, 641, 2137, 3011, 268207, ...	A001562
10	−3	2*, 3, 19, 31, 101, 139, 167, 1097, 43151, 60703, 90499, ...	A128069
10	−7	2*, 3, 5, 11, 19, 1259, 1399, 2539, 2843, 5857, 10589, ...
10	−9	4*, 7, 67, 73, 1091, 1483, 10937, ...	A217095
11	10	3, 5, 19, 311, 317, 1129, 4253, 7699, 18199, 35153, 206081, ...	A062577
11	9	5, 31, 271, 929, 2789, 4153, ...	A273601
11	8	2, 7, 11, 17, 37, 521, 877, 2423, ...	A273600
11	7	5, 19, 67, 107, 593, 757, 1801, 2243, 2383, 6043, 10181, 11383, 15629, ...	A273599
11	6	2, 3, 11, 163, 191, 269, 1381, 1493, ...	A273598
11	5	5, 41, 149, 229, 263, 739, 3457, 20269, 98221, ...	A128347
11	4	3, 5, 11, 17, 71, 89, 827, 22307, 45893, 63521, ...	A216181
11	3	3, 5, 19, 31, 367, 389, 431, 2179, 10667, 13103, 90397, ...	A128027
11	2	2, 5, 11, 13, 331, 599, 18839, 23747, 24371, 29339, 32141, 67421, ...	A210506
11	1	17, 19, 73, 139, 907, 1907, 2029, 4801, 5153, 10867, 20161, 293831, ...	A005808
11	−1	5, 7, 179, 229, 439, 557, 6113, 223999, 327001, ...	A057177
11	−2	3, 5, 17, 67, 83, 101, 1373, 6101, 12119, 61781, ...	A125957
11	−3	3, 103, 271, 523, 23087, 69833, ...	A128070
11	−4	2*, 7, 53, 67, 71, 443, 26497, ...	A224501
11	−5	7, 11, 181, 421, 2297, 2797, 4129, 4139, 7151, 29033, ...	A128340
11	−6	2*, 5, 7, 107, 383, 17359, 21929, 26393, ...
11	−7	7, 1163, 4007, 10159, ...
11	−8	2*, 3, 13, 31, 59, 131, 223, 227, 1523, ...
11	−9	2*, 3, 17, 41, 43, 59, 83, ...
11	−10	53, 421, 647, 1601, 35527, ...	A185239
12	11	2, 3, 7, 89, 101, 293, 4463, 70067, ...	A062578
12	7	2, 3, 7, 13, 47, 89, 139, 523, 1051, ...	A273814
12	5	2, 3, 31, 41, 53, 101, 421, 1259, 4721, 45259, ...	A128348
12	1	2, 3, 5, 19, 97, 109, 317, 353, 701, 9739, 14951, 37573, 46889, 769543, ...	A004064
12	−1	2*, 5, 11, 109, 193, 1483, 11353, 21419, 21911, 24071, 106859, 139739, ...	A057178
12	−5	2*, 3, 5, 13, 347, 977, 1091, 4861, 4967, 34679, ...	A128341
12	−7	2*, 3, 7, 67, 79, 167, 953, 1493, 3389, 4871, ...
12	−11	47, 401, 509, 8609, ...	A213216

^*Note: if b < 0 and n is even, then the numbers n are not included in the corresponding OEIS sequence.

A conjecture related to the generalized Mersenne primes: (the conjecture predicts where is the next generalized Mersenne prime, if the conjecture is true, then there are infinitely many primes for all such (a,b) pairs)

For any integers a and b which satisfy the conditions:

1. a > 1, −a < b < a.
2. a and b are coprime. (thus, b cannot be 0)
3. For every natural number r > 1, a and b are not both perfect rth powers. (since when a and b are both perfect rth powers, it can be shown that there are at most two n value such that aⁿ − bⁿ/a − b is prime, and these n values are r itself or a root of r, or 2)
4. −4ab is not a perfect fourth power (if so, then the number has aurifeuillean factorization).

has prime numbers of the form

$R_{p}(a,b)={\frac {a^{p}-b^{p}}{a-b}}$

for prime p, the prime numbers will be distributed near the best fit line

$Y=G\cdot \log _{a}(\log _{a}(R_{(a,b)}(n)))+C$

where

$\lim _{n\rightarrow \infty }G={\frac {1}{e^{\gamma }}}=0.561459483566\ldots$

and there are about

$(\log _{e}(N)+m\cdot \log _{e}(2)\cdot \log _{e}\left(\log _{e}(N))+{\frac {1}{\sqrt {N}}}-\delta \right)\cdot {\frac {e^{\gamma }}{\log _{e}(a)}}$

prime numbers of this form less than N.

• e is the base of the natural logarithm.
• γ is the Euler–Mascheroni constant.
• log_a is the logarithm in base a.
• R_(a,b)(n) is the nth prime number of the form a^p − b^p/a − b for prime p.
• C is a data fit constant which varies with a and b.
• δ is a data fit constant which varies with a and b.
• m is the largest natural number such that a and −b are both perfect 2^{m − 1}th powers.

We also have the following three properties:

1. The number of prime numbers of the form a^p − b^p/a − b (with prime p) less than or equal to n is about e^γ log_a(log_a(n)).
2. The expected number of prime numbers of the form a^p − b^p/a − b with prime p between n and an is about e^γ.
3. The probability that number of the form a^p − b^p/a − b is prime (for prime p) is about e^γ/p log_e(a).

If this conjecture is true, then for all such (a,b) pairs, let q be the nth prime of the form a^p − b^p/a − b, the graph of log_a(log_a(q)) versus n is almost linear. (See )

When a = b + 1, it is (b + 1)ⁿ − bⁿ, a difference of two consecutive perfect nth powers, and if aⁿ − bⁿ is prime, then a must be b + 1, because it is divisible by a − b.

Least n such that (b + 1)ⁿ − bⁿ is prime are

2, 2, 2, 3, 2, 2, 7, 2, 2, 3, 2, 17, 3, 2, 2, 5, 3, 2, 5, 2, 2, 229, 2, 3, 3, 2, 3, 3, 2, 2, 5, 3, 2, 3, 2, 2, 3, 3, 2, 7, 2, 3, 37, 2, 3, 5, 58543, 2, 3, 2, 2, 3, 2, 2, 3, 2, 5, 3, 4663, 54517, 17, 3, 2, 5, 2, 3, 3, 2, 2, 47, 61, 19, ... (sequence A058013 in the OEIS)

Least b such that (b + 1)^prime(n) − b^prime(n) is prime are

1, 1, 1, 1, 5, 1, 1, 1, 5, 2, 1, 39, 6, 4, 12, 2, 2, 1, 6, 17, 46, 7, 5, 1, 25, 2, 41, 1, 12, 7, 1, 7, 327, 7, 8, 44, 26, 12, 75, 14, 51, 110, 4, 14, 49, 286, 15, 4, 39, 22, 109, 367, 22, 67, 27, 95, 80, 149, 2, 142, 3, 11, ... (sequence A222119 in the OEIS)

See also

• Repunit
• Fermat prime
• Power of two
• Erdős–Borwein constant
• Mersenne conjectures
• Mersenne twister
• Double Mersenne number
• Prime95 / MPrime
• Great Internet Mersenne Prime Search (GIMPS)
• Largest known prime number
• Titanic prime
• Gigantic prime
• Megaprime
• Wieferich prime
• Wagstaff prime
• Cullen prime
• Woodall prime
• Proth prime
• Solinas prime
• Gillies' conjecture
• Williams number

External links

• "Mersenne number", Encyclopedia of Mathematics, EMS Press, 2001 [1994]
• GIMPS home page
• GIMPS status — status page gives various statistics on search progress, typically updated every week, including progress towards proving the ordering of the largest known Mersenne primes
• GIMPS, known factors of Mersenne numbers
• M_q = (8x)² − (3qy)² Property of Mersenne numbers with prime exponent that are composite (PDF)
• M_q = x² + d·y² math thesis (PS)
• Grime, James. "31 and Mersenne Primes". Numberphile. Brady Haran.
• Mersenne prime bibliography with hyperlinks to original publications
• report about Mersenne primes — detection in detail Template:De icon
• GIMPS wiki
• Will Edgington's Mersenne Page — contains factors for small Mersenne numbers
• Known factors of Mersenne numbers
• Decimal digits and English names of Mersenne primes
• Prime curios: 2305843009213693951
• Factorization of Mersenne numbers M_n, with n odd, n up to 1199
• Factorization of Mersenne numbers M_2n, 2n up to 2398 (n up to 1199) or 2n is in the form 8k + 4 up to 4796 (n is on the form 4k + 2 up to 2398)
• OEIS sequence A250197 (Numbers n such that the left Aurifeuillian primitive part of 2^n+1 is prime)—Factorization of Mersenne numbers M_n (n up to 1280)
• Factorization of completely factored Mersenne numbers
• The Cunningham project, factorization of bⁿ ± 1, b = 2, 3, 5, 6, 7, 10, 11, 12
• Factorization of bⁿ ± 1, 2 ≤ b ≤ 12
• Factorization of aⁿ ± bⁿ, with coprime a, b, 2 ≤ b < a ≤ 12

MathWorld links

• Weisstein, Eric W. "Mersenne number". MathWorld.
• Weisstein, Eric W. "Mersenne prime". MathWorld.
• 47th Mersenne Prime Found