A358699 a(n) is the largest prime factor of 2^(prime(n) - 1) - 1.

3, 5, 7, 31, 13, 257, 73, 683, 127, 331, 109, 61681, 5419, 2796203, 8191, 3033169, 1321, 599479, 122921, 38737, 22366891, 8831418697, 2931542417, 22253377, 268501, 131071, 28059810762433, 279073, 54410972897, 77158673929, 145295143558111, 2879347902817, 10052678938039

Offset: 2

Author

Hugo Pfoertner, Nov 27 2022

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 2..197 (terms 2..120 from Hugo Pfoertner)

Crossrefs

Cf. A005420, A006093, A006530, A061286, A071243, A086019, A098102.

Subsequence of A005420 and of A274906.

Programs

PARI

forprime (p=3, 140, my(f=factor(2^(p-1)-1)); print1(f[#f[,1],1],", "))

Python

from sympy import primefactors, sieve
def A358699(n): return primefactors(2**(sieve[n]-1)-1)[-1] # Karl-Heinz Hofmann, Nov 28 2022

Formula

a(n) = A006530(A098102(n)). - Michel Marcus, Nov 28 2022

a(n) = A005420(A006093(n)). - Amiram Eldar, Dec 01 2022