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%I #9 Mar 31 2012 13:22:09
%S 3,1,5,1,1,3,5,11,1,1,19,15,13,9,35,15,5,1,35,29,31,29,13,29,27,3,27,
%T 25,31,55,19,5,77,19,57,19,33,1,17,9,27,9,29,5,1,5,35,7,73,1,183,61,
%U 31,33,9,11,1,29,215,139,33,15,35,41,37,121,63,15,23,25
%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="/A187367/b187367.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, 70}]
%Y Cf. A187368, A187369, A187370, A187371.
%K nonn
%O 1,1
%A _Pierre CAMI_, Mar 09 2011
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