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 A253316 #17 Sep 03 2017 21:28:42 %S A253316 1,2,72,4140,4111116,48183195384 %N A253316 Number of 2n X 2n Takuzu grids. %C A253316 A Takuzu grid is a 2n X 2n zero-one matrix with the following properties: %C A253316 1. Every row and every column has n zeros and n ones. %C A253316 2. No row or column has three consecutive zeros or three consecutive ones. %C A253316 3. All rows are distinct, and all columns are distinct (but a row may be the same as a column). %H A253316 Wikipedia, <a href="http://en.wikipedia.org/wiki/Takuzu">Takuzu</a> %e A253316 The following is a 4 X 4 Takuzu grid: %e A253316 [ 0 1 1 0 ] %e A253316 [ 1 0 0 1 ] %e A253316 [ 0 0 1 1 ] %e A253316 [ 1 1 0 0 ] %Y A253316 Cf. A058527. %Y A253316 Number of possible rows equals A003440. %K A253316 nonn,more %O A253316 0,2 %A A253316 _Brian Kell_, Dec 30 2014 %E A253316 a(5) from _Frans J. Faase_, Dec 14 2015