A242016 - OEIS

%I #21 Oct 11 2019 02:18:07

%S 3,3,3,7,3,23,3,3,7,3,3,3,7,3,47,3,31,3,7,3,233,3,3,7,3,31,3,223,3,7,

%T 3,13367,3,431,3,7,3,2351,3,127,3,7,3,6361,3,23,3,7,3,179951,3,3,7,3,

%U 31,3,193707721,3,7,3

%N Smallest prime factor of A135972(n), the n-th composite Mersenne number.

%H Chai Wah Wu, <a href="/A242016/b242016.txt">Table of n, a(n) for n = 1..1201</a>

%F a(n) = A020639(A135972(n)).

%o (PARI) for(n=2, 1e2, if(!ispseudoprime(2^n-1), p=factor(2^n-1)[1, 1]; print1(p, ", ")))

%Y Cf. A135972, A242017. Subsequence of A056608.

%K nonn

%O 1,1

%A _Felix Fröhlich_, Aug 11 2014