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 A269102 #7 Apr 19 2020 23:47:57 %S A269102 4,180,40908,43964700,232068730044,6206909793496236, %T A269102 858502190008810133292,622342168717398556687064028, %U A269102 2386083493285894017930101786679468 %N A269102 Number of n X n 0..3 arrays with some element plus some horizontally or vertically adjacent neighbor totalling three no more than once. %C A269102 Diagonal of A269109. %H A269102 R. H. Hardin, <a href="/A269102/b269102.txt">Table of n, a(n) for n = 1..11</a> %e A269102 Some solutions for n=3 %e A269102 ..0..1..3. .3..1..0. .3..1..3. .0..0..2. .0..2..3. .2..0..1. .0..0..0 %e A269102 ..0..2..2. .2..1..0. .2..0..1. .1..2..0. .1..3..3. .0..1..0. .0..1..0 %e A269102 ..2..0..2. .2..0..0. .3..3..3. .0..2..2. .1..1..2. .2..0..2. .2..3..3 %Y A269102 Cf. A269109. %K A269102 nonn %O A269102 1,1 %A A269102 _R. H. Hardin_, Feb 19 2016