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 A268743 #7 Apr 19 2020 23:42:05 %S A268743 2,11,143,4110,255651,34732937,10319681062,6744840113811, %T A268743 9736268648482947,31152408949342676906,221573405414594347811555, %U A268743 3511390061199964238627005057,124222798189336185449669887550302 %N A268743 Number of n X n binary arrays with some element plus some horizontally or vertically adjacent neighbor totalling two no more than once. %C A268743 Diagonal of A268750. %H A268743 R. H. Hardin, <a href="/A268743/b268743.txt">Table of n, a(n) for n = 1..26</a> %e A268743 Some solutions for n=4 %e A268743 ..0..0..1..0. .0..1..1..0. .1..0..0..0. .0..0..0..1. .1..0..0..1 %e A268743 ..1..0..0..1. .0..0..0..0. .0..0..1..0. .0..1..0..0. .0..0..0..0 %e A268743 ..0..0..0..0. .0..1..0..1. .0..0..0..1. .0..1..0..1. .0..0..1..0 %e A268743 ..0..0..0..0. .0..0..0..0. .0..1..0..1. .1..0..0..0. .1..1..0..0 %Y A268743 Cf. A268750. %K A268743 nonn %O A268743 1,1 %A A268743 _R. H. Hardin_, Feb 12 2016