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 A187116 #6 Mar 30 2012 18:37:26
%S A187116 1,4,20,138,1258,14476,202655,3354848,64246776,1398909332,34157026526,
%T A187116 924757926320,27503093599024,891534666547216,31289986924954924,
%U A187116 1182213869836721036,47846600590876178320,2065282617724684345208
%N A187116 A diagonal of triangle A187115.
%C A187116 Definition of triangle: A187115(n,k) = [y^k] R_{n-1}(y+y^2) for k=2..n, n>2, where R_n(y) is the n-th row polynomial with R_2(y)=y^2.
%F A187116 Equals column 1 in the matrix square of triangle A135080.
%o A187116 (PARI) {a(n)=local(Rn=y^2);for(m=2,n+1,Rn=subst(truncate(Rn),y,y+y^2+O(y^m)));polcoeff(Rn,n,y)}
%Y A187116 Cf. A187115, A135082, A187117, A187118, A187119.
%K A187116 nonn
%O A187116 2,2
%A A187116 _Paul D. Hanna_, Mar 08 2011