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 A094172 #6 Mar 31 2012 10:32:25 %S A094172 0,0,0,21,390,3427,18380,73413,237459,659774,1629116,3666785,7651680 %N A094172 Number of quasi-pentominoes in an n X n bounding box. %H A094172 Erich Friedman, <a href="/A094172/a094172.gif">Illustration of initial terms</a> %e A094172 See A094170 for example of similar sequence. %Y A094172 Cf. A094170, A094171. %K A094172 nonn %O A094172 0,4 %A A094172 _Jon Wild_, May 07 2004 %E A094172 Corrected and extended by _Jon Wild_, May 11 2004