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 A268802 #7 Apr 19 2020 23:44:04 %S A268802 3,34,332,5848,195384,12432856,1508087180,348686105792, %T A268802 154172619407288,130573457756588328,212323461305457440492, %U A268802 663970589813116610557692,3999438097971983178736358520,46462227980008803491191644654968 %N A268802 Number of n X n 0..2 arrays with some element plus some horizontally, vertically or antidiagonally adjacent neighbor totalling two not more than once. %C A268802 Diagonal of A268809. %H A268802 R. H. Hardin, <a href="/A268802/b268802.txt">Table of n, a(n) for n = 1..18</a> %e A268802 Some solutions for n=4 %e A268802 ..2..2..2..2. .0..0..1..2. .2..1..0..0. .0..1..0..0. .1..2..2..1 %e A268802 ..1..1..2..2. .1..2..2..2. .2..0..0..0. .1..0..0..0. .2..2..2..2 %e A268802 ..2..2..2..2. .2..2..1..2. .1..0..0..1. .0..0..0..1. .1..2..2..1 %e A268802 ..1..2..1..2. .2..2..2..2. .0..0..0..0. .0..0..0..0. .2..1..2..1 %Y A268802 Cf. A268809. %K A268802 nonn %O A268802 1,1 %A A268802 _R. H. Hardin_, Feb 13 2016