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 A215873 #7 Jul 22 2025 23:26:13 %S A215873 1,1,1,4,20,189,1642,26451,307874,7027942,98057806,2850280812, %T A215873 44974137856 %N A215873 Number of permutations of 0..floor((5*n-2)/2) on odd squares of an 5Xn array such that each row, column, diagonal and (downwards) antidiagonal of odd squares is increasing. %C A215873 Row 5 of A215870 %e A215873 Some solutions for n=5 %e A215873 ..x..0..x..2..x....x..0..x..1..x....x..0..x..1..x....x..0..x..2..x %e A215873 ..1..x..3..x..5....2..x..3..x..5....2..x..3..x..5....1..x..3..x..5 %e A215873 ..x..4..x..7..x....x..4..x..7..x....x..4..x..6..x....x..4..x..6..x %e A215873 ..6..x..8..x..9....6..x..8..x.10....7..x..8..x.10....7..x..8..x..9 %e A215873 ..x.10..x.11..x....x..9..x.11..x....x..9..x.11..x....x.10..x.11..x %K A215873 nonn %O A215873 1,4 %A A215873 _R. H. Hardin_ Aug 25 2012