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 A107029 #3 Mar 30 2012 18:59:07
%S A107029 1,1,3,3,5,7,11,19,35,69,151,339,829,2111,5607,15737,45289,136477,
%T A107029 423279,1353671,4471673,15114479,52605755,187162155,681817179,
%U A107029 2539492249,9646349779,37415172217,147745308403,594368656811
%N A107029 Diagonal sums of number triangle A107027.
%F A107029 a(n)=sum{k=0..floor(n/2), (n-2k-1)C((n-2k)*k, k)-(n-2k-2)*sum{j=0..k, C((n-2k)*k, j)}}
%K A107029 easy,nonn
%O A107029 0,3
%A A107029 _Paul Barry_, May 09 2005