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 A056634 #6 Mar 30 2012 16:48:51 %S A056634 1,24,342,3804,36802,326540,2735308,22006264,171912401,1313614776, %T A056634 9868281330,73150450248,536495354621,3900954906412,28164962681150, %U A056634 202166363020920,1444068530799525,10272599729628876 %N A056634 Number of polygons of length 2n with one hole on square lattice (not allowing rotations). %H A056634 I. Jensen, <a href="/A056634/b056634.txt">Table of n, a(n) for n = 8..41</a> (from link below) %H A056634 I. Jensen, <a href="http://www.ms.unimelb.edu.au/~iwan/polygons/series/square.perim.1hole.ser">More terms</a> %Y A056634 Cf. A002931. %K A056634 nonn %O A056634 8,2 %A A056634 _N. J. A. Sloane_, Aug 30 2000