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 A269269 #7 Apr 19 2020 23:48:17 %S A269269 0,108,46872,74853576,542973139128,19356924219624936, %T A269269 3516906597130333936872,3322606082327701612506093240, %U A269269 16524782213263820847479975782463640 %N A269269 Number of n X n 0..3 arrays with some element plus some horizontally or antidiagonally adjacent neighbor totalling three exactly once. %C A269269 Diagonal of A269276. %H A269269 R. H. Hardin, <a href="/A269269/b269269.txt">Table of n, a(n) for n = 1..11</a> %e A269269 Some solutions for n=3 %e A269269 ..2..3..1. .0..2..3. .1..3..3. .2..0..0. .3..1..2. .3..3..1. .2..3..0 %e A269269 ..3..1..1. .3..3..3. .0..1..1. .2..2..1. .0..2..2. .2..3..2. .1..0..0 %e A269269 ..2..0..0. .2..0..1. .0..0..1. .3..1..0. .3..3..1. .1..1..0. .1..1..0 %Y A269269 Cf. A269276. %K A269269 nonn %O A269269 1,2 %A A269269 _R. H. Hardin_, Feb 21 2016