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 A266452 #5 Aug 12 2016 07:04:21 %S A266452 1,1,5,101,3417,184881,14216101,1477674733,199405047857, %T A266452 33889007175041,7081268215880805,1784184251089927605 %N A266452 Number of nX2 arrays containing 2 copies of 0..n-1 with no element 1 greater than its north neighbor modulo n and the upper left element equal to 0. %C A266452 Column 2 of A266455. %e A266452 Some solutions for n=4 %e A266452 ..0..1....0..0....0..2....0..3....0..3....0..3....0..2....0..3....0..2....0..1 %e A266452 ..2..3....3..3....2..0....0..3....2..3....0..1....3..0....2..3....2..1....3..1 %e A266452 ..0..1....1..2....1..3....2..1....2..1....2..1....1..3....1..2....1..3....2..3 %e A266452 ..2..3....1..2....3..1....2..1....1..0....2..3....1..2....0..1....0..3....0..2 %Y A266452 Cf. A266455. %K A266452 nonn %O A266452 1,3 %A A266452 _R. H. Hardin_, Dec 29 2015