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%I #7 Mar 31 2012 13:22:09
%S 1,1,1,1,3,1,5,19,9,1,11,13,13,11,21,1,15,5,41,41,39,17,7,1,25,1,27,
%T 51,13,11,47,39,37,39,1,45,15,5,23,13,59,5,47,175,35,11,53,15,19,131,
%U 41,1,45,17,1,53,83,49,85,159,123,69,23,29,23,207,37,19,37,39,91,13,57
%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 0.8.
%H Pierre CAMI, <a href="/A187369/b187369.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, A187370, A187371.
%K nonn
%O 1,5
%A _Pierre CAMI_, Mar 09 2011
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