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 A129356 #3 Mar 30 2012 18:37:03
%S A129356 1,-3,-3,15,-15,66,-261,618,-1155,1040,2361,-11616,23733,-27027,29394,
%T A129356 -132318,545790,-1383459,2418896,-3383679,4278462,-3127320,-8332866,
%U A129356 42021990,-99069516,160683318,-200247795,214883010,-345461022,1184850729,-3966311448,9899287254,-18787986009
%N A129356 G.f.: A(x) = Product_{n>=1} [ (1-x)^3*(1 + 3x + 6x^2 +...+ n(n+1)/2*x^(n-1)) ].
%C A129356 a(k) != 0 (mod 3) at k = 9*A001318(n) for n>=0, where A001318 are the generalized pentagonal numbers: m(3m-1)/2, m=0,+-1,+-2,...; a(k) == 1 (mod 3) at k = 9*A036498(n) (n>=0); a(k) == -1 (mod 3) at k = 9*A036499(n) (n>=0).
%F A129356 G.f.: A(x) = Product_{n>=1} [ 1 - (n+1)(n+2)/2*x^n + n(n+2)*x^(n+1) - n(n+1)/2*x^(n+2) ].
%e A129356 A(x) = (1-3x+3x^2-x^3)(1-6x^2+8x^3-3x^4)(1-10x^3+15x^4-6x^5)*...
%e A129356 *( 1 - (n+1)(n+2)/2*x^n + n(n+2)*x^(n+1) - n(n+1)/2*x^(n+2) )*...
%e A129356 Terms are divisible by 3 except at positions given by:
%e A129356 a(n) == 1 (mod 3) at n = [0, 45, 63, 198, 234, 459,...,9*A036498(k),..];
%e A129356 a(n) == -1 (mod 3) at n = [9, 18, 108, 135, 315, 360,..,9*A036499(k),..].
%o A129356 (PARI) {a(n)=if(n==0,1,polcoeff(prod(k=1,n,(1-x)^3*sum(j=1,k,j*(j+1)/2*x^(j-1)) +x*O(x^n)),n))}
%Y A129356 Cf. A129355, A129357, A129358; A001318, A036498, A036499.
%K A129356 sign
%O A129356 0,2
%A A129356 _Paul D. Hanna_, Apr 10 2007