%I A113036
%S A113036 0,0,1,2,0,0,8,13,0,0,69,123,0,0,719,1313,0,0,8215,15260,0,0,99774,
%T A113036 187615,0,0,1264854,2399207,0,0,16544234,31587644,0,0,221625505,
%U A113036 425313967,0,0,3025271756,5829531261,0,0,41929052284,81066732018,0
%N A113036 Number of solutions to +- 1 +- 2 +- .. +- n = 2.
%F A113036 a(n) is the coefficient of x^2 in product(x^(-k)+x^k, k=1..n).
%p A113036 A113036:= proc(n) local i,j,p,t; t:= NULL; for j to n do p:=1; for i 
               to j do p:=p*(x^(-i)+x^i); od; t:=t,coeff(p,x,2); od; t; end;
%Y A113036 Cf. A058377, A063865, A063866.
%Y A113036 Sequence in context: A058347 A058547 A134414 this_sequence A000425 A010893 
               A000171
%Y A113036 Adjacent sequences: A113033 A113034 A113035 this_sequence A113037 A113038 
               A113039
%K A113036 nonn
%O A113036 1,4
%A A113036 Floor van Lamoen (fvlamoen(AT)hotmail.com),Oct 11 2005