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 A125690 #7 Sep 08 2013 19:59:15 %S A125690 1,1,1,3,1,1,5,5,1,1,11,9,7,1,1,21,25,13,9,1,1,43,53,43,17,11,1,1,85, %T A125690 125,97,65,21,13,1,1,171,273,255,153,91,25,15,1,1,341,609,597,441,221, %U A125690 121,29,17,1,1,683,1325,1443 %N A125690 Riordan array (1/(1-x-2x^2), x(1-x)/(1-x-2x^2)). %C A125690 First column is A001045. Row sums are Pell numbers A000129(n+1). Diagonal sums are A125691. %F A125690 G.f.: 1/(1-x-2x^2-xy(1-x)). %F A125690 T(n,k) = T(n-1,k) + T(n-1,k-1) + 2*T(n-2,k) - T(n-2,k-1). - _Philippe Deléham_, Feb 24 2012 %e A125690 Triangle begins %e A125690 1, %e A125690 1, 1, %e A125690 3, 1, 1, %e A125690 5, 5, 1, 1, %e A125690 11, 9, 7, 1, 1, %e A125690 21, 25, 13, 9, 1, 1, %e A125690 43, 53, 43, 17, 11, 1, 1 %K A125690 easy,nonn,tabl %O A125690 0,4 %A A125690 _Paul Barry_, Nov 30 2006