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 A228749 #9 Dec 18 2015 18:18:39 %S A228749 1,3,39,780,43862,4823826,1316714732,762713002760,1040109467257908, %T A228749 3118624187066762728,21501868781585259257676, %U A228749 331091404725670052219822756,11603262095526618070600084170304,914315533886530112431287075923892544 %N A228749 Number of n X n binary arrays with top left element equal to 1 and no two ones adjacent horizontally or antidiagonally. %C A228749 Diagonal of A228754 %H A228749 R. H. Hardin, <a href="/A228749/b228749.txt">Table of n, a(n) for n = 1..30</a> %e A228749 Some solutions for n=4 %e A228749 ..1..0..0..0....1..0..0..1....1..0..0..0....1..0..1..0....1..0..0..0 %e A228749 ..1..0..0..0....0..1..0..0....0..0..0..1....0..0..1..0....1..0..1..0 %e A228749 ..0..1..0..1....0..0..0..1....0..1..0..0....1..0..0..1....1..0..1..0 %e A228749 ..0..1..0..0....1..0..0..0....0..1..0..1....0..0..0..0....1..0..0..0 %K A228749 nonn %O A228749 1,2 %A A228749 _R. H. Hardin_ Sep 02 2013