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 A269029 #7 Apr 19 2020 23:46:13 %S A269029 0,24,348,18384,1326576,208867428,63310818360,40013955378312, %T A269029 51911512873697772,140039775591497709312,791864652110724378938904, %U A269029 9334169232033820587188999592,232675011644185023762453520339476 %N A269029 Number of n X n 0..2 arrays with some element plus some horizontally, diagonally or antidiagonally adjacent neighbor totalling two exactly once. %C A269029 Diagonal of A269035. %H A269029 R. H. Hardin, <a href="/A269029/b269029.txt">Table of n, a(n) for n = 1..14</a> %e A269029 Some solutions for n=4 %e A269029 ..2..2..2..2. .2..1..0..0. .2..1..0..2. .2..1..2..2. .0..1..2..1 %e A269029 ..2..2..2..1. .0..0..0..0. .0..1..2..1. .0..1..2..1. .2..1..0..2 %e A269029 ..1..2..2..1. .0..0..0..0. .2..1..0..1. .0..1..2..1. .0..1..2..1 %e A269029 ..2..1..2..1. .1..0..0..0. .2..1..2..1. .2..2..2..2. .0..1..2..2 %Y A269029 Cf. A269035. %K A269029 nonn %O A269029 1,2 %A A269029 _R. H. Hardin_, Feb 18 2016