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 A107269 #3 Mar 30 2012 18:59:07
%S A107269 1,0,1,1,3,6,16,44,136,457,1669,6547,27334,120465,557094,2692528,
%T A107269 13564940,71102869,387132791,2185813423,12775466408,77154694819,
%U A107269 480630407368,3083443893896,20344187534051,137884769704754
%N A107269 Diagonal sums of A107267, viewed as a number triangle.
%F A107269 a(n)=sum{k=0..n, sum{j=0..n-2k, (1/(j+1))C(j+1, n-2k-j+1)C(n-2k, j)k^j}}
%K A107269 easy,nonn
%O A107269 0,5
%A A107269 _Paul Barry_, May 15 2005