A197119 - OEIS

%I #19 Sep 21 2019 08:28:19

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

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

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

%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 1 to n / n tends to 2.00.

%H Pierre CAMI, <a href="/A197119/b197119.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, A197118.

%K nonn

%O 1,3

%A _Pierre CAMI_, Oct 11 2011