A187370 - OEIS

%I #7 Mar 31 2012 13:22:09

%S 1,3,1,5,9,3,21,3,1,11,13,5,27,27,7,5,27,3,27,41,13,11,49,5,69,83,61,

%T 47,9,21,3,3,45,35,21,21,3,3,7,39,9,3,27,51,73,35,27,33,27,125,103,

%U 255,27,63,207,171,153,27,3,105,147

%N Least odd number k such that (k*2^n+1)*k*2^n + 1 is prime.

%C As N increases, it appears that (sum_{k=1..N} a(k)) / (sum_{k=1..N} k) tends to 1.25.

%H Pierre CAMI, <a href="/A187370/b187370.txt">Table of n, a(n) for n = 1..4000</a>

%t Table[k = 1; While[! PrimeQ[(k*2^n + 1)*k*2^n + 1], k = k + 2]; k, {n, 100}]

%Y Cf. A187367, A187368, A187369, A187371.

%K nonn

%O 1,2

%A _Pierre CAMI_, Mar 09 2011