A197117 - OEIS

%I #17 Sep 21 2019 08:28:06

%S 1,2,0,3,1,2,0,3,2,2,0,3,1,4,0,3,2,5,2,4,2,1,1,2,3,2,1,2,2,3,0,4,2,4,

%T 1,2,4,7,0,4,3,3,0,4,5,1,0,3,2,2,1,1,2,2,0,2,3,2,1,4,0,5,0,2,5,4,0,7,

%U 4,2,2,7,0,3,1,2,0,5,0,2,3,1,0,4,4,0,0,1,0,8

%N Number of k such that (2^k-1)*2^n+1 is prime with 0 < k < n+1.

%C As n increases sum a(n) from n=1 to n / n tends to 2.66.

%H Pierre CAMI, <a href="/A197117/b197117.txt">Table of n, a(n) for n = 1..3000</a>

%o (PARI) a(n) = sum(k=1, n, isprime((2^k-1)*2^n+1)); \\ _Michel Marcus_, Sep 21 2019

%Y Cf. A197116, A197118, A197119.

%K nonn

%O 1,2

%A _Pierre CAMI_, Oct 11 2011