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 A175564 #4 Apr 21 2019 20:58:31 %S A175564 1,2,14,156,840,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, %T A175564 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, %U A175564 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0 %N A175564 Number of n X n binary matrices that contain no 2 X 2 submatrix consisting of all zeros or all ones. %F A175564 For n >= 5, a(n) = 0. %Y A175564 Cf. A175563. %K A175564 easy,nonn %O A175564 0,2 %A A175564 _Max Alekseyev_, Jul 03 2010