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 A264639 #5 Mar 07 2022 13:55:10 %S A264639 1,3,28,400,7776,229392,9082368,481406976,30249676800,2458667520000, %T A264639 229405685760000 %N A264639 Number of 2 X n arrays of permutations of 0..n*2-1 with rows nondecreasing modulo 2 and columns nondecreasing modulo 4. %C A264639 Row 2 of A264638. %e A264639 Some solutions for n=4 %e A264639 ..4..2..6..5....4..0..6..5....2..0..4..5....4..0..2..1....2..0..4..1 %e A264639 ..0..3..7..1....2..3..7..1....6..7..3..1....6..5..3..7....6..7..5..3 %Y A264639 Cf. A264638. %K A264639 nonn %O A264639 1,2 %A A264639 _R. H. Hardin_, Nov 19 2015