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 A098511 #3 Mar 30 2012 18:58:59
%S A098511 1,1,3,6,21,54,186,479,1938,5795,22888,70781,286443,861463,3592105,
%T A098511 11492256,39274353,148852401,613876868,1917516257,8511689170,
%U A098511 25445125513,100975365920,390096404027,1666653892303,5319341488465
%N A098511 Diagonal sums of a matrix associated to the inverse of a Catalan scaled binomial matrix.
%C A098511 Diagonal sums of A098509.
%F A098511 a(n)=sum{k=0..floor(n/2), denominator((n-k+1)Binomial(n-k, k)/Binomial(2(n-k), n-k))}
%K A098511 easy,nonn
%O A098511 0,3
%A A098511 _Paul Barry_, Sep 11 2004