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%I #17 Sep 21 2019 08:28:11
%S 1,2,2,3,0,4,2,3,1,4,1,4,2,1,2,5,0,5,1,2,2,4,2,4,1,3,0,6,2,4,0,4,1,3,
%T 3,4,1,4,3,2,0,5,7,1,0,5,1,5,0,1,3,7,2,8,3,4,1,4,2,8,0,3,5,6,0,7,2,2,
%U 1,1,2,8,1,2,1,7,0,2,0,3,0,5,0,4,1,2,2,6,1,4
%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 2.66.
%H Pierre CAMI, <a href="/A197118/b197118.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, A197119.
%K nonn
%O 1,2
%A _Pierre CAMI_, Oct 11 2011
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