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 A269504 #5 Aug 12 2016 07:05:19 %S A269504 1,14,420,18332,1261420,134871120,21338020496 %N A269504 Number of nX3 arrays containing 3 copies of 0..n-1 avoiding the pattern down-up in every row and column. %C A269504 Column 3 of A269505. %e A269504 Some solutions for n=4 %e A269504 ..0..0..3. .0..2..1. .0..2..1. .2..2..1. .0..2..1. .0..0..1. .0..0..1 %e A269504 ..1..1..2. .0..3..1. .1..2..2. .0..2..3. .1..2..3. .3..2..2. .3..2..2 %e A269504 ..2..3..1. .1..3..3. .3..3..3. .0..3..1. .3..3..2. .1..3..2. .2..3..1 %e A269504 ..3..2..0. .0..2..2. .0..0..1. .1..3..0. .0..0..1. .1..3..0. .0..3..1 %Y A269504 Cf. A269505. %K A269504 nonn %O A269504 1,2 %A A269504 _R. H. Hardin_, Feb 28 2016