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 A075221 #11 Dec 05 2014 02:43:50 %S A075221 1,1,1,3,4,12,21,56,111,262,462,1453,1875,4734,9410,20603,24034,79352, %T A075221 79925,273731,358096,669640,796571,3342349,2980476,6387513,10167660, %U A075221 24999509,21477012,87978317 %N A075221 Number of polyiamonds with n cells that tile the plane by translation or by 180-degree rotation (Conway criterion). %D A075221 Branko Grünbaum and G. C. Shephard, Tilings and Patterns. W. H. Freeman, New York, 1987, Section 9.4. %H A075221 Joseph Myers, <a href="http://www.polyomino.org.uk/mathematics/polyform-tiling/">Polyiamond tiling</a> %Y A075221 Cf. A071332, A075216, A075217, A075218, A075219, A075220, A075222, A075223, A075224, A075203, A075212. %K A075221 hard,nonn %O A075221 1,4 %A A075221 _Joseph Myers_, Sep 08 2002 %E A075221 More terms from _Joseph Myers_, Nov 11 2003 %E A075221 a(29) and a(30) from _Joseph Myers_, Nov 21 2010