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 A225621 #13 Aug 05 2013 13:45:24 %S A225621 1,4,20,108,632,4060,28968,231000,2058096,20375964,222393800, %T A225621 2653879624,34365597840,479776469848,7181892528272,114731622081840, %U A225621 1948073992109280,35031456100431900,665075537735997960,13292908401187179240,279000321119414475600 %N A225621 Central terms of the triangle in A074911. %C A225621 a(n) = A074911(2*n-1,n). %o A225621 (Haskell) %o A225621 a225621 n = a074911 (2 * n - 1) n %Y A225621 Cf. A227791. %K A225621 nonn %O A225621 1,2 %A A225621 _Reinhard Zumkeller_, Aug 05 2013