A187368 - OEIS

%I #8 Mar 31 2012 13:22:09

%S 1,1,9,1,9,7,3,9,39,31,5,25,3,15,27,9,39,7,3,19,9,45,29,7,11,15,51,79,

%T 23,67,35,1,21,85,63,21,29,39,9,9,53,13,29,39,69,115,5,9,3,51,41,9,9,

%U 109,15,15,63,31,95,195,81,15,207,63,63,43,105,57,141,163,53

%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="/A187368/b187368.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, A187369, A187370, A187371.

%K nonn

%O 1,3

%A _Pierre CAMI_, Mar 09 2011