A074479 Largest prime factor of 5^n - 1.

2, 3, 31, 13, 71, 31, 19531, 313, 829, 521, 12207031, 601, 305175781, 19531, 1741, 11489, 466344409, 5167, 3981071, 9161, 519499, 12207031, 332207361361, 390001, 9384251, 305175781, 31051, 234750601, 22125996444329, 7621

Offset: 1

Author

Rick L. Shepherd, Aug 23 2002

Keywords

• nonn

Examples

			5^9 - 1 = 1953124 = (2^2)*19*31*829, so a(9) = 829.
		

Links

• Table of n, a(n) for n = 1..502
• S. S. Wagstaff, Jr., The Cunningham Project

Crossrefs

Cf. A074478 (largest prime factor of 5^n + 1), A074477 (largest prime factor of 3^n - 1), A074249 (largest prime factor of 7^n - 1).

Cf. A006530, A024049.

Cf. similar sequences listed in A274906.

Programs

Magma

[Maximum(PrimeDivisors(5^n-1)): n in [1..45]]; // Vincenzo Librandi, Jul 13 2016

Mathematica

Table[FactorInteger[5^n - 1] [[-1, 1]], {n, 30}] (* Vincenzo Librandi, Aug 23 2013 *)

PARI

for(n=1,32, v=factor(5^n-1); print1(v[matsize(v)[1],1],","))

Formula

a(n) = A006530(A024049(n)). - Vincenzo Librandi, Jul 13 2016

Extensions

Terms to a(100) in b-file from Vincenzo Librandi, Aug 23 2013

a(101)-a(448) in b-file from Amiram Eldar, Feb 01 2020

a(449)-a(502) in b-file from Max Alekseyev, Apr 25 2022