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 A107031 #3 Mar 30 2012 18:59:07
%S A107031 1,2,3,4,7,12,25,56,145,422,1389,5072,20283,87996,412663,2087868,
%T A107031 11361831,66155642,409567833,2680486870,18465061963,133504614880,
%U A107031 1011121118741,8008145020804,66201411633209,570006877641976
%N A107031 Diagonal sums of number triangle A107030.
%F A107031 a(n)=sum{k=0..floor(n/2), (k-1)*C(k(n-2k), n-2k)-(k-2)*sum{j=0..n-k, C(k(n-2k), j)}}
%K A107031 easy,nonn
%O A107031 0,2
%A A107031 _Paul Barry_, May 09 2005