%I #5 May 01 2013 21:16:01
%S 9,231,3999,65151,1047039,16771071,268410879,4294868991,68719083519,
%T 1099510054911,17592179752959,281474951544831,4503599526707199,
%U 72057593635274751,1152921502996234239,18446744067267100671
%N a(n)=16^n - 3*2^(2*n - 1) - 1.
%C Idea resulted from seqfan posts by _Artur Jasinski_.
%F a(n)=16^n - 3*2^(2*n - 1) - 1=(2^(2*n - 1) - 1)*(2^(2*n + 1) + 1).
%t b[n_] := 16^n - 3*2^(2*n - 1) - 1. Table[b[n], {n, 1, 30}]
%K nonn
%O 1,1
%A _Roger L. Bagula_, Nov 24 2008
%E Definition corrected by _N. J. A. Sloane_, Dec 22 2009 (these are not semiprimes).