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 A131910 #2 Mar 30 2012 18:37:04 %S A131910 1,1,3,8,26,79,274,964,3496,12664,46157,168240,615173,2256669,8321911, %T A131910 30871862,115280183,433247309,1638036186,6225871432,23769249188, %U A131910 91077899373,350002189936,1348065993111,5201249282212,20094668668700 %N A131910 Central terms of triangle A131909. %F A131910 a(n) = A131909(2n,n) for n>=0. %o A131910 (PARI) %Y A131910 Cf. A131909. %K A131910 nonn %O A131910 0,3 %A A131910 _Paul D. Hanna_, Jul 26 2007