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 A109970 #3 Mar 30 2012 18:59:08 %S A109970 1,0,1,0,-2,1,0,1,-4,1,0,0,6,-6,1,0,0,-4,15,-8,1,0,0,1,-20,28,-10,1,0, %T A109970 0,0,15,-56,45,-12,1,0,0,0,-6,70,-120,66,-14,1,0,0,0,1,-56,210,-220, %U A109970 91,-16,1,0,0,0,0,28,-252,495,-364,120,-18,1 %N A109970 Riordan array (1,x(1-x)^2). %C A109970 Row sums are A077954. Diagonal sums are (-1)^n*A094686(n). Matrix inverse is A109971. %F A109970 G.f.: 1/(1-xy(1-x)^2); Number triangle T(n, k)=binomial(2k, n-k)*(-1)^(n-k). %e A109970 Rows begin %e A109970 1; %e A109970 0,1; %e A109970 0,-2,1; %e A109970 0,1,-4,1; %e A109970 0,0,6,-6,1; %e A109970 0,0,-4,15,-8,1; %e A109970 0,0,1,-20,28,-10,1; %e A109970 0,0,0,15,-56,45,-12,1; %K A109970 easy,sign,tabl %O A109970 0,5 %A A109970 _Paul Barry_, Jul 06 2005