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 A075202 #12 Dec 05 2014 03:05:09 %S A075202 1,1,2,5,12,35,101,320,960,2701,6164,19770,34918,94023,232714,462463, %T A075202 770010,2462890,3247171,9756012,18463420,32963374,51599559,177923609, %U A075202 236127160 %N A075202 Number of polyominoes with n cells that tile the plane by 180-degree rotation (Conway criterion). %D A075202 Branko Grünbaum and G. C. Shephard, Tilings and Patterns. W. H. Freeman, New York, 1987, Section 9.4. %H A075202 Joseph Myers, <a href="http://www.polyomino.org.uk/mathematics/polyform-tiling/">Polyomino tiling</a> %Y A075202 Cf. A054359, A075198, A075199, A075200, A075201, A075203, A075204, A075205, A075206, A075211, A075220. %K A075202 hard,nonn %O A075202 1,3 %A A075202 _Joseph Myers_, Sep 08 2002 %E A075202 More terms from _Joseph Myers_, Nov 04 2003 %E A075202 a(24) and a(25) from _Joseph Myers_, Nov 17 2010