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 A228500 #9 Dec 18 2015 18:18:39 %S A228500 1,1,12,87,2002,59839,3862849,405580157,81304395949,28446567810005, %T A228500 18268841726936268,20937720031330292269,43502129718103134992611, %U A228500 162426195975365708781849519,1095156092719874995442597502324 %N A228500 Number of n X n binary arrays with top left value 1 and no two ones adjacent horizontally, vertically, diagonally or antidiagonally. %C A228500 Diagonal of A228506 %H A228500 R. H. Hardin, <a href="/A228500/b228500.txt">Table of n, a(n) for n = 1..29</a> %e A228500 Some solutions for n=4 %e A228500 ..1..0..0..1....1..0..0..1....1..0..0..0....1..0..1..0....1..0..0..0 %e A228500 ..0..0..0..0....0..0..0..0....0..0..0..0....0..0..0..0....0..0..0..1 %e A228500 ..1..0..0..1....0..1..0..1....0..0..0..0....0..0..1..0....0..0..0..0 %e A228500 ..0..0..0..0....0..0..0..0....0..1..0..0....1..0..0..0....0..0..0..1 %K A228500 nonn %O A228500 1,3 %A A228500 _R. H. Hardin_ Aug 23 2013