This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A129355 #3 Mar 30 2012 18:37:03
%S A129355 1,-2,-2,4,-1,12,-26,38,-51,6,98,-190,138,60,132,-1296,2990,-3738,
%T A129355 3350,-3752,4077,1194,-12272,18528,-14848,9018,-2002,5644,-86729,
%U A129355 290596,-514158,611070,-603150,657792,-952808,1406568,-1208636,-635286,3507362,-5062866,3791614
%N A129355 G.f.: A(x) = Product_{n>=1} [ (1-x)^2*(1 + 2x + 3x^2 +...+ n*x^(n-1)) ].
%C A129355 a(k) == 1 (mod 2) at k = 4*A001318(n) for n>=0, where A001318 are the generalized pentagonal numbers: m(3m-1)/2, m=0,+-1,+-2,....
%F A129355 G.f.: A(x) = Product_{n>=1} ( 1 - (n+1)*x^n + n*x^(n+1) ) . G.f.: A(x) = Product_{n>=1} [ (1-x)*(1 + x + x^2 +...+ x^(n-1) - n*x^n) ] .
%e A129355 A(x) = (1 - 2x + x^2)(1 - 3x^2 + 2x^3)(1 - 4x^3 + 3x^4)(1 - 5x^4 + 4x^5)*...
%e A129355 Terms are even except at positions given by:
%e A129355 a(n) == 1 (mod 2) at n = [0, 4, 8, 20, 28, 48, 60, 88,...,4*A001318(n),...].
%o A129355 (PARI) a(n)=if(n==0,1,polcoeff(prod(k=1,n,1-(k+1)*x^k+k*x^(k+1)+x*O(x^n)),n))
%Y A129355 Cf. A129356, A129357, A129358.
%K A129355 sign
%O A129355 0,2
%A A129355 _Paul D. Hanna_, Apr 10 2007