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 A267899 #5 Aug 12 2016 07:05:19 %S A267899 1,3,20,138,1488,20400,317520,5911920,126080640,2999566080,79604985600 %N A267899 Number of nX3 arrays containing 3 copies of 0..n-1 with every element equal to at least one horizontal or vertical neighbor and the top left element equal to 0. %C A267899 Column 3 of A267901. %e A267899 Some solutions for n=4 %e A267899 ..0..0..1....0..0..0....0..0..0....0..0..1....0..1..1....0..0..3....0..2..2 %e A267899 ..0..1..1....2..3..3....1..1..1....2..0..1....0..1..2....0..3..3....0..0..2 %e A267899 ..2..2..3....2..3..1....2..2..2....2..2..1....0..2..2....1..1..1....3..1..1 %e A267899 ..2..3..3....2..1..1....3..3..3....3..3..3....3..3..3....2..2..2....3..3..1 %Y A267899 Cf. A267901. %K A267899 nonn %O A267899 1,2 %A A267899 _R. H. Hardin_, Jan 22 2016