A367005 a(n) is the largest prime factor of n*2^n+1 for n>0, and a(0)=1.

1, 3, 3, 5, 13, 23, 11, 23, 683, 419, 19, 1733, 199, 11833, 487, 997, 61681, 4691, 211, 5279, 7541, 1914791, 7177, 607, 5233, 6689, 2373919, 336823, 8937209, 6051013, 409, 11681, 25781083, 6031230671, 18803, 32502455213, 934861, 339016085231, 55586743

Offset: 0

Author

Sean A. Irvine, Oct 31 2023

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 0..865

Crossrefs

Cf. A002064, A006530, A005420, A367003, A367004.

Programs

Mathematica

A367005[n_]:=FactorInteger[n*2^n+1][[-1,1]];Array[A367005,50,0] (* Paolo Xausa, Nov 09 2023 *)

Formula

a(n) = A006530(A002064(n)).

Extensions

Name edited by Michel Marcus, Nov 10 2023