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 A269187 #6 Apr 20 2020 19:50:52 %S A269187 4,108,9284,2817548,3159954052,13377149358556,217602949665911156, %T A269187 13760950074226562086140,3411379570274317633099847884, %U A269187 3335382860394625859139269051079788 %N A269187 Number of n X n 0..3 arrays with some element plus some horizontally, diagonally, antidiagonally or vertically adjacent neighbor totalling three no more than once. %C A269187 Diagonal of A269194. %e A269187 Some solutions for n=3 %e A269187 ..0..0..0. .2..2..0. .0..1..0. .2..2..2. .3..3..3. .1..3..2. .0..1..3 %e A269187 ..2..0..2. .3..2..0. .0..0..0. .0..0..2. .3..2..2. .1..1..3. .1..3..1 %e A269187 ..3..2..0. .3..2..0. .0..0..1. .0..2..0. .0..2..3. .3..3..3. .1..3..3 %Y A269187 Cf. A269194. %K A269187 nonn %O A269187 1,1 %A A269187 _R. H. Hardin_, Feb 20 2016