OFFSET
1,3
COMMENTS
In the first 3100 terms: if a(n) > 0 its average is about 3; for less than 9% of n is a(n) = 0.
LINKS
Pierre CAMI, Table of n, a(n) for n = 1..3100
MATHEMATICA
Table[Length[Select[Range[n - 1], PrimeQ[4^n - 2^# - 1] &]], {n, 100}] (* T. D. Noe, May 03 2012 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Pierre CAMI, Apr 28 2012
STATUS
approved