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 A049689 #5 Mar 30 2012 18:56:56
%S A049689 0,0,1,0,3,0,5,0,9,0,13,0,17,0,23,0,31,0,37,0,45,0,55,0,63,0,75,0,87,
%T A049689 0,95,0,111,0,127,0,139,0,157,0,173,0
%N A049689 a(n)=Sum{((-1)^(i+1))*T(i,n-i): i=0,1,...,n}, array T as in A049687.
%K A049689 nonn
%O A049689 0,5
%A A049689 _Clark Kimberling_