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 A215791 #8 May 04 2025 15:08:26 %S A215791 1,1,1,4,25,189,2465,26451,530429,7027942,187205626,2850280812 %N A215791 Number of permutations of 0..floor((5*n-1)/2) on even squares of an 5*n array such that each row, column, diagonal and (downwards) antidiagonal of even squares is increasing. %e A215791 Some solutions for n=5: %e A215791 ..0..x..1..x..4....0..x..1..x..4....0..x..1..x..3....0..x..1..x..3 %e A215791 ..x..2..x..5..x....x..2..x..5..x....x..2..x..4..x....x..2..x..5..x %e A215791 ..3..x..6..x..8....3..x..6..x..8....5..x..6..x..8....4..x..6..x..8 %e A215791 ..x..7..x..9..x....x..7..x.10..x....x..7..x..9..x....x..7..x..9..x %e A215791 .10..x.11..x.12....9..x.11..x.12...10..x.11..x.12...10..x.11..x.12 %Y A215791 Row 5 of A215788. %K A215791 nonn,more %O A215791 1,4 %A A215791 _R. H. Hardin_, Aug 23 2012