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 A075203 #12 Dec 05 2014 03:04:56 %S A075203 1,1,2,5,12,35,101,320,961,2703,6174,19905,35060,94614,235381,467754, %T A075203 776873,2498766,3281990,9917824,18735749,33417839,52251279,181365462, %U A075203 239569893 %N A075203 Number of polyominoes with n cells that tile the plane by translation or by 180-degree rotation (Conway criterion). %D A075203 Branko Grünbaum and G. C. Shephard, Tilings and Patterns. W. H. Freeman, New York, 1987, Section 9.4. %H A075203 Joseph Myers, <a href="http://www.polyomino.org.uk/mathematics/polyform-tiling/">Polyomino tiling</a> %Y A075203 Cf. A054359, A075198, A075199, A075200, A075201, A075202, A075204, A075205, A075206, A075212, A075221. %K A075203 hard,nonn %O A075203 1,3 %A A075203 _Joseph Myers_, Sep 08 2002 %E A075203 More terms from _Joseph Myers_, Nov 04 2003 %E A075203 a(24) and a(25) from _Joseph Myers_, Nov 17 2010