Aurifeuillean factorization

In number theory, an aurifeuillean factorization, or aurifeuillian factorization, named after Léon-François-Antoine Aurifeuille, is a special type of algebraic factorization that comes from non-trivial factorizations of cyclotomic polynomials over the integers.^[1] Although cyclotomic polynomials themselves are irreducible over the integers, when restricted to particular integer values they may have an algebraic factorization, as in the examples below.

Examples

Numbers of the form $2^{4k+2}+1$ have the following aurifeuillean factorization:^[2]

2^{4k+2}+1=(2^{2k+1}-2^{k+1}+1)\cdot (2^{2k+1}+2^{k+1}+1)

Numbers of the form $b^{n}-1$ $b^{n}-1$ or $\Phi _{n}(b)$ $\Phi _{n}(b)$ , where $b=s^{2}\cdot t$ $b=s^{2}\cdot t$ with square-free $t$ $t$ , have aurifeuillean factorization if and only if one of the following conditions holds:
- $t\equiv 1{\pmod {4}}$ and $n\equiv t{\pmod {2t}}$
- $t\equiv 2,3{\pmod {4}}$ and $n\equiv 2t{\pmod {4t}}$

Thus, when

b=s^{2}\cdot t

with square-free

t

, and

n

is congruent to

t

mod

2t

, then if

t

is congruent to 1 mod 4,

b^{n}-1

have aurifeuillean factorization, otherwise,

b^{n}+1

have aurifeuillean factorization.

When the number is of a particular form (the exact expression varies with the base), Aurifeuillian factorization may be used, which gives a product of two or three numbers. The following equations give Aurifeuillian factors for the Cunningham project bases as a product of F, L and M:^[3]

If we let L = A - B, M = A + B, the Aurifeuillian factorizations for bⁿ ± 1 with the base 2 ≤ b ≤ 24 (perfect powers excluded, since a power of bⁿ is also a power of b) are:

(Number = F * (A - B) * (A + B) = F * L * M)

b	Number	F	A	B
2	2^{4k + 2} + 1	1	2^{2k + 1} + 1	2^{k + 1}
3	3^{6k + 3} + 1	3^{2k + 1} + 1	3^{2k + 1} + 1	3^{k + 1}
5	5^{10k + 5} - 1	5^{2k + 1} - 1	5^{4k + 2} + 3(5^{2k + 1}) + 1	5^{3k + 2} + 5^{k + 1}
6	6^{12k + 6} + 1	6^{4k + 2} + 1	6^{4k + 2} + 3(6^{2k + 1}) + 1	6^{3k + 2} + 6^{k + 1}
7	7^{14k + 7} + 1	7^{2k + 1} + 1	7^{6k + 3} + 3(7^{4k + 2}) + 3(7^{2k + 1}) + 1	7^{5k + 3} + 7^{3k + 2} + 7^{k + 1}
10	10^{20k + 10} + 1	10^{4k + 2} + 1	10^{8k + 4} + 5(10^{6k + 3}) + 7(10^{4k + 2}) + 5(10^{2k + 1}) + 1	10^{7k + 4} + 2(10^{5k + 3}) + 2(10^{3k + 2}) + 10^{k + 1}
11	11^{22k + 11} + 1	11^{2k + 1} + 1	11^{10k + 5} + 5(11^{8k + 4}) - 11^{6k + 3} - 11^{4k + 2} + 5(11^{2k + 1}) + 1	11^{9k + 5} + 11^{7k + 4} - 11^{5k + 3} + 11^{3k + 2} + 11^{k + 1}
12	12^{6k + 3} + 1	12^{2k + 1} + 1	12^{2k + 1} + 1	6(12^k)
13	13^{26k + 13} - 1	13^{2k + 1} - 1	13^{12k + 6} + 7(13^{10k + 5}) + 15(13^{8k + 4}) + 19(13^{6k + 3}) + 15(13^{4k + 2}) + 7(13^{2k + 1}) + 1	13^{11k + 6} + 3(13^{9k + 5}) + 5(13^{7k + 4}) + 5(13^{5k + 3}) + 3(13^{3k + 2}) + 13^{k + 1}
14	14^{28k + 14} + 1	14^{4k + 2} + 1	14^{12k + 6} + 7(14^{10k + 5}) + 3(14^{8k + 4}) - 7(14^{6k + 3}) + 3(14^{4k + 2}) + 7(14^{2k + 1}) + 1	14^{11k + 6} + 2(14^{9k + 5}) - 14^{7k + 4} - 14^{5k + 3} + 2(14^{3k + 2}) + 14^{k + 1}
15	15^{30k + 15} + 1	15^{14k + 7} - 15^{12k + 6} + 15^{10k + 5} + 15^{4k + 2} - 15^{2k + 1} + 1	15^{8k + 4} + 8(15^{6k + 3}) + 13(15^{4k + 2}) + 8(15^{2k + 1}) + 1	15^{7k + 4} + 3(15^{5k + 3}) + 3(15^{3k + 2}) + 15^{k + 1}
17	17^{34k + 17} - 1	17^{2k + 1} - 1	17^{16k + 8} + 9(17^{14k + 7}) + 11(17^{12k + 6}) - 5(17^{10k + 5}) - 15(17^{8k + 4}) - 5(17^{6k + 3}) + 11(17^{4k + 2}) + 9(17^{2k + 1}) + 1	17^{15k + 8} + 3(17^{13k + 7}) + 17^{11k + 6} - 3(17^{9k + 5}) - 3(17^{7k + 4}) + 17^{5k + 3} + 3(17^{3k + 2}) + 17^{k + 1}
18	18^{4k + 2} + 1	1	18^{2k + 1} + 1	6(18^k)
19	19^{38k + 19} + 1	19^{2k + 1} + 1	19^{18k + 9} + 9(19^{16k + 8}) + 17(19^{14k + 7}) + 27(19^{12k + 6}) + 31(19^{10k + 5}) + 31(19^{8k + 4}) + 27(19^{6k + 3}) + 17(19^{4k + 2}) + 9(19^{2k + 1}) + 1	19^{17k + 9} + 3(19^{15k + 8}) + 5(19^{13k + 7}) + 7(19^{11k + 6}) + 7(19^{9k + 5}) + 7(19^{7k + 4}) + 5(19^{5k + 3}) + 3(19^{3k + 2}) + 19^{k + 1}
20	20^{10k + 5} - 1	20^{2k + 1} - 1	20^{4k + 2} + 3(20^{2k + 1}) + 1	10(20^{3k + 1}) + 10(20^k)
21	21^{42k + 21} - 1	21^{18k + 9} + 21^{16k + 8} + 21^{14k + 7} - 21^{4k + 2} - 21^{2k + 1} - 1	21^{12k + 6} + 10(21^{10k + 5}) + 13(21^{8k + 4}) + 7(21^{6k + 3}) + 13(21^{4k + 2}) + 10(21^{2k + 1}) + 1	21^{11k + 6} + 3(21^{9k + 5}) + 2(21^{7k + 4}) + 2(21^{5k + 3}) + 3(21^{3k + 2}) + 21^{k + 1}
22	22^{44k + 22} + 1	22^{4k + 2} + 1	22^{20k + 10} + 11(22^{18k + 9}) + 27(22^{16k + 8}) + 33(22^{14k + 7}) + 21(22^{12k + 6}) + 11(22^{10k + 5}) + 21(22^{8k + 4}) + 33(22^{6k + 3}) + 27(22^{4k + 2}) + 11(22^{2k + 1}) + 1	22^{19k + 10} + 4(22^{17k + 9}) + 7(22^{15k + 8}) + 6(22^{13k + 7}) + 3(22^{11k + 6}) + 3(22^{9k + 5}) + 6(22^{7k + 4}) + 7(22^{5k + 3}) + 4(22^{3k + 2}) + 22^{k + 1}
23	23^{46k + 23} + 1	23^{2k + 1} + 1	23^{22k + 11} + 11(23^{20k + 10}) + 9(23^{18k + 9}) - 19(23^{16k + 8}) - 15(23^{14k + 7}) + 25(23^{12k + 6}) + 25(23^{10k + 5}) - 15(23^{8k + 4}) - 19(23^{6k + 3}) + 9(23^{4k + 2}) + 11(23^{2k + 1}) + 1	23^{21k + 11} + 3(23^{19k + 10}) - 23^{17k + 9} - 5(23^{15k + 8}) + 23^{13k + 7} + 7(23^{11k + 6}) + 23^{9k + 5} - 5(23^{7k + 4}) - 23^{5k + 3} + 3(23^{3k + 2}) + 23^{k + 1}
24	24^{12k + 6} + 1	24^{4k + 2} + 1	24^{4k + 2} + 3(24^{2k + 1}) + 1	12(24^{3k + 1}) + 12(24^k)

(See ^[4] for more information (square-free bases up to 199))

In fact, L * M =

\Phi _{n}(b^{2k+1})

, where

b=s^{2}\cdot t

with square-free

t

, and n = t if t is congruent to 1 mod 4. Otherwise, n = 2t.

Numbers of the form $a^{4}+4b^{4}$ have the following aurifeuillean factorization:

a^{4}+4b^{4}=(a^{2}-2ab+2b^{2})\cdot (a^{2}+2ab+2b^{2}).

Lucas number $L_{10k+5}$ have the following aurifeuillean factorization:

L_{10k+5}=L_{2k+1}\cdot (5{F_{2k+1}}^{2}-5F_{2k+1}+1)\cdot (5{F_{2k+1}}^{2}+5F_{2k+1}+1)

where

L_{n}

is the

n

th Lucas number,

F_{n}

is the

n

th Fibonacci number.

History

In 1871, Aurifeuille discovered the factorization of $2^{4k+2}+1$ for k = 14 as the following:^[2]^[5]

2^{58}+1=536838145\cdot 536903681.\,\!

The second factor is prime, and the factorization of the first factor is $5\cdot 107367629.$ ^[5] The general form of the factorization was later discovered by Lucas.^[2]

References

^ A. Granville, P. Pleasants (2006). "Aurifeuillian factorization" (PDF). Math. Comp. 75: 497–508. doi:10.1090/S0025-5718-05-01766-7.
^ ^a ^b ^c Weisstein, Eric W. "Aurifeuillean Factorization". MathWorld.
^ "Main Cunningham Tables". Retrieved 21 December 2015. At the end of tables 2LM, 3+, 5-, 7+, 10+, 11+ and 12+ are formulae detailing the Aurifeuillian factorisations.
^ List of Aurifeuillean factorization
^ ^a ^b Integer Arithmetic, Number Theory – Aurifeuillian Factorizations, Numericana

External links

Aurifeuillian Factorisation, Colin Barker
Online factor collection

[1] A. Granville, P. Pleasants (2006). "Aurifeuillian factorization" (PDF). Math. Comp. 75: 497–508. doi:10.1090/S0025-5718-05-01766-7.

[Wolfram-2] Weisstein, Eric W. "Aurifeuillean Factorization". MathWorld.

[3] "Main Cunningham Tables". Retrieved 21 December 2015. At the end of tables 2LM, 3+, 5-, 7+, 10+, 11+ and 12+ are formulae detailing the Aurifeuillian factorisations.

[4] List of Aurifeuillean factorization

[numericana-5] Integer Arithmetic, Number Theory – Aurifeuillian Factorizations, Numericana

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