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 A075218 #11 Dec 05 2014 02:42:54 %S A075218 1,2,8,24,61,269,501,2121,4709,14978,26675,123081,179707,660366, %T A075218 1479114 %N A075218 Number of polyiamonds with 2n cells that tile the plane both by translation and by 180-degree rotation (Conway criterion). %C A075218 Polyiamonds with an odd number of cells have different numbers of triangles with the two orientations and so cannot tile by translation. %D A075218 Branko Grünbaum and G. C. Shephard, Tilings and Patterns. W. H. Freeman, New York, 1987, Section 9.4. %H A075218 Joseph Myers, <a href="http://www.polyomino.org.uk/mathematics/polyform-tiling/">Polyiamond tiling</a> %Y A075218 Cf. A071332, A075216, A075217, A075219, A075220, A075221, A075222, A075223, A075224, A075200, A075209. %K A075218 hard,nonn %O A075218 1,2 %A A075218 _Joseph Myers_, Sep 08 2002 %E A075218 More terms from _Joseph Myers_, Nov 11 2003 %E A075218 a(15) (30-iamonds) from _Joseph Myers_, Nov 21 2010