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 A056639 #6 Mar 30 2012 16:48:51 %S A056639 62,3920,130560,3058544,56925214,900355884,12619939046,161208191596, %T A056639 1913821820768,21416926011756,228320059956022,2337581305737496, %U A056639 23128907576991302,222266054948571020,2082868947950189248 %N A056639 Number of polygons of length 2n with 3 (self-avoiding polygon) holes on square lattice (not allowing rotations). %H A056639 I. Jensen, <a href="/A056639/b056639.txt">Table of n, a(n) for n = 16..45</a> (from link below) %H A056639 I. Jensen, <a href="http://www.ms.unimelb.edu.au/~iwan/polygons/series/square.perim.3hole.ser">More terms</a> %Y A056639 Cf. A002931. %K A056639 nonn %O A056639 16,1 %A A056639 _N. J. A. Sloane_, Aug 30 2000