A197118 - OEIS

%I #17 Sep 21 2019 08:28:11

%S 1,2,2,3,0,4,2,3,1,4,1,4,2,1,2,5,0,5,1,2,2,4,2,4,1,3,0,6,2,4,0,4,1,3,

%T 3,4,1,4,3,2,0,5,7,1,0,5,1,5,0,1,3,7,2,8,3,4,1,4,2,8,0,3,5,6,0,7,2,2,

%U 1,1,2,8,1,2,1,7,0,2,0,3,0,5,0,4,1,2,2,6,1,4

%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 1 to n / n tends to 2.66.

%H Pierre CAMI, <a href="/A197118/b197118.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, A197117, A197119.

%K nonn

%O 1,2

%A _Pierre CAMI_, Oct 11 2011