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 A126157 #5 Sep 08 2013 13:31:00
%S A126157 1,5,55,1415,69025,5403005,616437655,96365988815,19756766836225,
%T A126157 5140259013390005,1654190282113104055,645005323804145184215,
%U A126157 299613583126435893179425,163464903833408195554809005
%N A126157 Main diagonal and central terms of symmetric triangle A126155.
%F A126157 a(n)=Sum_{k, 0<=k<=n}A130847(n,k)*4^k. - _Philippe Deléham_, Jul 22 2007
%Y A126157 Cf. A126155; A126156 (column 0), A126158 (diagonal).
%K A126157 nonn
%O A126157 0,2
%A A126157 _Paul D. Hanna_, Dec 20 2006