A074249 a(n) = largest prime factor of 7^n-1.

3, 3, 19, 5, 2801, 43, 4733, 1201, 1063, 2801, 293459, 181, 16148168401, 4733, 159871, 169553, 2767631689, 117307, 4534166740403, 4021, 11898664849, 10746341, 31479823396757, 1201, 31280679788951, 16148168401, 2583253

Offset: 1

Author

N. J. A. Sloane, Sep 26 2002

Keywords

• nonn

Links

• Table of n, a(n) for n = 1..388

Crossrefs

Cf. A006530, A024075, A057954, A059889, A085032.

Programs

Mathematica

Join[{1}, Table[FactorInteger[7^n - 1] [[-1, 1]], {n, 30}]] (* Vincenzo Librandi, Aug 23 2012 *)

PARI

a(n) = vecmax(factor(7^n-1)[,1]); \\ Michel Marcus, Dec 16 2017

Formula

a(n) = A006530(A024075(n)). - Michel Marcus, Dec 16 2017

Extensions

More terms from Benoit Cloitre, Sep 29 2002

Terms to a(80) in b-file from Vincenzo Librandi, Aug 23 2013

a(81)-a(378) in b-file from Amiram Eldar, Feb 02 2020

a(0) removed and a(379)-a(388) in b-file added by Max Alekseyev, Apr 25 2022, Sep 11 2022