Catalan's conjecture

For Catalan's aliquot sequence conjecture, see Aliquot sequence § Catalan–Dickson conjecture.

For Catalan's Mersenne number conjecture, see Double Mersenne number § Catalan–Mersenne number conjecture.

Catalan's conjecture (or Mihăilescu's theorem) is a theorem in number theory that was conjectured by the mathematician Eugène Charles Catalan in 1844 and proven in 2002 by Preda Mihăilescu at Paderborn University. The integers 2³ and 3² are two perfect powers (that is, powers of exponent higher than one) of natural numbers whose values (8 and 9, respectively) are consecutive. The theorem states that this is the only case of two consecutive perfect powers. That is to say, that

Catalan's conjecture — the only solution in the natural numbers of

$x^{a}-y^{b}=1$

for a, b > 1, x, y > 0 is x = 3, a = 2, y = 2, b = 3.

History

The history of the problem dates back at least to Gersonides, who proved a special case of the conjecture in 1343 where (x, y) was restricted to be (2, 3) or (3, 2). The first significant progress after Catalan made his conjecture came in 1850 when Victor-Amédée Lebesgue dealt with the case b = 2.

In 1976, Robert Tijdeman applied Baker's method in transcendence theory to establish a bound on a,b and used existing results bounding x,y in terms of a, b to give an effective upper bound for x,y,a,b. Michel Langevin computed a value of $\exp \exp \exp \exp 730\approx 10^{10^{10^{10^{317}}}}$ for the bound, resolving Catalan's conjecture for all but a finite number of cases.

Catalan's conjecture was proven by Preda Mihăilescu in April 2002. The proof was published in the Journal für die reine und angewandte Mathematik, 2004. It makes extensive use of the theory of cyclotomic fields and Galois modules. An exposition of the proof was given by Yuri Bilu in the Séminaire Bourbaki. In 2005, Mihăilescu published a simplified proof.

Pillai's conjecture

Unsolved problem in mathematics:

Does each positive integer occur only finitely many times as a difference of perfect powers?

(more unsolved problems in mathematics)

Pillai's conjecture concerns a general difference of perfect powers (sequence A001597 in the OEIS): it is an open problem initially proposed by S. S. Pillai, who conjectured that the gaps in the sequence of perfect powers tend to infinity. This is equivalent to saying that each positive integer occurs only finitely many times as a difference of perfect powers: more generally, in 1931 Pillai conjectured that for fixed positive integers A, B, C the equation $Ax^{n}-By^{m}=C$ has only finitely many solutions (x, y, m, n) with (m, n) ≠ (2, 2). Pillai proved that the difference $|Ax^{n}-By^{m}|\gg x^{\lambda n}$ for any λ less than 1, uniformly in m and n.

The general conjecture would follow from the ABC conjecture.

Paul Erdős conjectured that the ascending sequence $(a_{n})_{n\in \mathbb {N} }$ of perfect powers satisfies $a_{n+1}-a_{n}>n^{c}$ for some positive constant c and all sufficiently large n.

Pillai's conjecture means that for every natural number n, there are only finitely many pairs of perfect powers with difference n. The list below shows, for n ≤ 64, all solutions for perfect powers less than 10¹⁸, as OEIS: A076427. See also OEIS: A103953 for the smallest solution (> 0).

n	solution count	numbers k such that k and k + n are both perfect powers		n	solution count	numbers k such that k and k + n are both perfect powers
1	1	8		33	2	16, 256
2	1	25		34	0	none
3	2	1, 125		35	3	1, 289, 1296
4	3	4, 32, 121		36	2	64, 1728
5	2	4, 27		37	3	27, 324, 14348907
6	0	none		38	1	1331
7	5	1, 9, 25, 121, 32761		39	4	25, 361, 961, 10609
8	3	1, 8, 97336		40	4	9, 81, 216, 2704
9	4	16, 27, 216, 64000		41	3	8, 128, 400
10	1	2187		42	0	none
11	4	16, 25, 3125, 3364		43	1	441
12	2	4, 2197		44	3	81, 100, 125
13	3	36, 243, 4900		45	4	4, 36, 484, 9216
14	0	none		46	1	243
15	3	1, 49, 1295029		47	6	81, 169, 196, 529, 1681, 250000
16	3	9, 16, 128		48	4	1, 16, 121, 21904
17	7	8, 32, 64, 512, 79507, 140608, 143384152904		49	3	32, 576, 274576
18	3	9, 225, 343		50	0	none
19	5	8, 81, 125, 324, 503284356		51	2	49, 625
20	2	16, 196		52	1	144
21	2	4, 100		53	2	676, 24336
22	2	27, 2187		54	2	27, 289
23	4	4, 9, 121, 2025		55	3	9, 729, 175561
24	5	1, 8, 25, 1000, 542939080312		56	4	8, 25, 169, 5776
25	2	100, 144		57	3	64, 343, 784
26	3	1, 42849, 6436343		58	0	none
27	3	9, 169, 216		59	1	841
28	7	4, 8, 36, 100, 484, 50625, 131044		60	4	4, 196, 2515396, 2535525316
29	1	196		61	2	64, 900
30	1	6859		62	0	none
31	2	1, 225		63	4	1, 81, 961, 183250369
32	4	4, 32, 49, 7744		64	4	36, 64, 225, 512

See also

• Beal's conjecture
• Equation x^y = y^x
• Fermat–Catalan conjecture
• Mordell curve
• Ramanujan–Nagell equation
• Størmer's theorem
• Tijdeman's theorem

References

• Bilu, Yuri (2004), "Catalan's conjecture (after Mihăilescu)", Astérisque, 294: vii, 1–26, MR 2111637
• Catalan, Eugene (1844), "Note extraite d'une lettre adressée à l'éditeur", J. Reine Angew. Math. (in French), 27: 192, doi:10.1515/crll.1844.27.192, MR 1578392
• Cohen, Henri (2005). Démonstration de la conjecture de Catalan [A proof of the Catalan conjecture]. Théorie algorithmique des nombres et équations diophantiennes (in French). Palaiseau: Éditions de l'École Polytechnique. pp. 1–83. ISBN 2-7302-1293-0. MR 0222434.
• Metsänkylä, Tauno (2004), "Catalan's conjecture: another old Diophantine problem solved" (PDF), Bulletin of the American Mathematical Society, 41 (1): 43–57, doi:10.1090/S0273-0979-03-00993-5, MR 2015449
• Mihăilescu, Preda (2004), "Primary Cyclotomic Units and a Proof of Catalan's Conjecture", J. Reine Angew. Math., 2004 (572): 167–195, doi:10.1515/crll.2004.048, MR 2076124
• Mihăilescu, Preda (2005), "Reflection, Bernoulli numbers and the proof of Catalan's conjecture" (PDF), European Congress of Mathematics, Zurich: Eur. Math. Soc.: 325–340, MR 2185753
• Ribenboim, Paulo (1994), Catalan's Conjecture, Boston, MA: Academic Press, Inc., ISBN 0-12-587170-8, MR 1259738 Predates Mihăilescu's proof.
• Tijdeman, Robert (1976), "On the equation of Catalan" (PDF), Acta Arith., 29 (2): 197–209, doi:10.4064/aa-29-2-197-209, MR 0404137

External links

• Weisstein, Eric W. "Catalan's conjecture". MathWorld.
• Ivars Peterson's MathTrek
• On difference of perfect powers
• Jeanine Daems: A Cyclotomic Proof of Catalan's Conjecture