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 A269477 #5 Aug 12 2016 07:04:23 %S A269477 1,6,54,600,9102,188472,5118012,172101936,6887210886,321643938456 %N A269477 Number of nX2 arrays containing 2 copies of 0..n-1 avoiding the pattern down-up in every row and equal-up in every column. %C A269477 Column 2 of A269479. %e A269477 Some solutions for n=4 %e A269477 ..1..0. .2..1. .2..1. .2..3. .2..1. .1..1. .3..0. .0..2. .3..0. .3..1 %e A269477 ..2..2. .3..0. .0..1. .3..1. .2..1. .2..0. .1..3. .3..3. .3..2. .2..0 %e A269477 ..3..3. .2..0. .0..2. .2..1. .3..0. .2..0. .1..2. .2..1. .1..2. .2..0 %e A269477 ..1..0. .1..3. .3..3. .0..0. .3..0. .3..3. .0..2. .1..0. .0..1. .3..1 %Y A269477 Cf. A269479. %K A269477 nonn %O A269477 1,2 %A A269477 _R. H. Hardin_, Feb 27 2016