%I #41 Dec 01 2022 12:40:56

%S 3,5,7,31,13,257,73,683,127,331,109,61681,5419,2796203,8191,3033169,

%T 1321,599479,122921,38737,22366891,8831418697,2931542417,22253377,

%U 268501,131071,28059810762433,279073,54410972897,77158673929,145295143558111,2879347902817,10052678938039

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

%H Amiram Eldar, <a href="/A358699/b358699.txt">Table of n, a(n) for n = 2..197</a> (terms 2..120 from Hugo Pfoertner)

%F a(n) = A006530(A098102(n)). - _Michel Marcus_, Nov 28 2022

%F a(n) = A005420(A006093(n)). - _Amiram Eldar_, Dec 01 2022

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

%o (Python)

%o from sympy import primefactors, sieve

%o def A358699(n): return primefactors(2**(sieve[n]-1)-1)[-1] # _Karl-Heinz Hofmann_, Nov 28 2022

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

%Y Subsequence of A005420 and of A274906.

%K nonn

%O 2,1

%A _Hugo Pfoertner_, Nov 27 2022