%I A086256
%S A086256 0,0,0,0,0,0,0,0,0,1,1,0,0,1,1,1,0,1,0,2,1,4,1,2,1,1,0,13,4,5,0,2,2,1,
               1,
%T A086256 13,1,1,4,7,1,11,4,14,9,4,4,28,0,12,11,12,4,2,5,28,4,26,1,63,0,1,5,12,
               1,
%U A086256 29,1,12,2,44,4,101,4,11,27,12,1,26,4,15,4,11,1,75,1,11,14,36,0,40,11
%N A086256 Number of base-2 Fermat pseudoprimes that divide 2^n-1.
%C A086256 A base-2 Fermat pseudoprime is a composite number x such that 2^x = 2 
               mod x.
%H A086256 Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/
               Pseudoprime.html">Pseudoprime</a>
%F A086256 a(n) = Sum{d|n} A086249(d), the Mobius transform of A086249.
%t A086256 Table[d=Divisors[2^n-1]; cnt=0; Do[m=d[[i]]; If[ !PrimeQ[m]&&PowerMod[2, 
               m, m]==2, cnt++ ], {i, Length[d]}]; cnt, {n, 100}]
%Y A086256 Cf. A001567 (base-2 pseudoprimes), A086249.
%Y A086256 Sequence in context: A140168 A059119 A127772 this_sequence A057550 A059150 
               A133186
%Y A086256 Adjacent sequences: A086253 A086254 A086255 this_sequence A086257 A086258 
               A086259
%K A086256 hard,nonn
%O A086256 1,20
%A A086256 T. D. Noe (noe(AT)sspectra.com), Jul 14 2003