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 A094171 #6 Mar 31 2012 10:32:25 %S A094171 0,0,1,20,147,670,2239,6138,14531,30904,60369,110300,190671,314910, %T A094171 500247,768810,110300,190671,314910,500247,768810,1147959,1671648 %N A094171 Number of quasi-tetrominoes in an n X n bounding box. %H A094171 Erich Friedman, <a href="/A094171/a094171.gif">Illustration of initial terms</a> %e A094171 See A094170 for example of similar sequence. %Y A094171 Cf. A094170, A094172. %K A094171 nonn %O A094171 0,4 %A A094171 _Jon Wild_, May 07 2004 %E A094171 Corrected and extended by _Jon Wild_, May 11 2004