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 A269145 #6 Apr 20 2020 19:50:01 %S A269145 0,80,13904,7002040,12637025328,88082672552208,2456638851763181776, %T A269145 279573979783982763379528,131383670545605944288719844352, %U A269145 256961574793195204388371517319842144 %N A269145 Number of n X n 0..3 arrays with some element plus some horizontally, antidiagonally or vertically adjacent neighbor totalling three exactly once. %C A269145 Diagonal of A269152. %e A269145 Some solutions for n=3 %e A269145 ..2..2..2. .1..1..1. .3..3..2. .1..1..0. .0..2..3. .2..2..3. .2..2..1 %e A269145 ..3..3..1. .3..3..1. .3..3..2. .1..0..1. .2..3..1. .3..1..1. .2..0..1 %e A269145 ..1..1..1. .3..3..2. .3..3..1. .2..0..0. .3..2..0. .1..3..3. .2..0..0 %Y A269145 Cf. A269152. %K A269145 nonn %O A269145 1,2 %A A269145 _R. H. Hardin_, Feb 20 2016