Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #18 May 03 2012 15:11:53
%S 0,1,2,1,2,3,2,2,5,5,4,4,2,0,2,3,0,6,3,3,4,3,2,4,0,1,2,3,0,5,1,3,4,1,
%T 2,6,2,2,1,6,0,2,3,1,5,2,5,3,4,2,6,5,1,3,4,6,3,4,2,1,4,2,2,3,6,2,4,4,
%U 7,4,2,8,2,0,4,4,1,1,5,2,5,2,4,10,1,0,5
%N Number of primes of the form 4^n - 2^k - 1 with 0 < k < n.
%C In the first 3100 terms: if a(n) > 0 its average is about 3; for less than 9% of n is a(n) = 0.
%H Pierre CAMI, <a href="/A182413/b182413.txt">Table of n, a(n) for n = 1..3100</a>
%t Table[Length[Select[Range[n - 1], PrimeQ[4^n - 2^# - 1] &]], {n, 100}] (* _T. D. Noe_, May 03 2012 *)
%K nonn
%O 1,3
%A _Pierre CAMI_, Apr 28 2012