OFFSET
1,2
COMMENTS
EXAMPLE
3^1-2^0 = 2 which is prime, so a(1)=1
3^3-{2^4,2^3,2^2,2^1,2^0} = {11,19,23,25,26}, three of which are prime, so a(3) = 3
MATHEMATICA
np[n_]:=Module[{p2=2^Range[0, Floor[Log[2, 3^n]]]}, Count[3^n-p2, _?PrimeQ]]; Array[np, 110] (* Harvey P. Dale, Nov 06 2012 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Carl R. White, Oct 23 2010
STATUS
approved