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 A187631 #6 Jul 22 2025 10:51:03 %S A187631 64,2924,14044,31903442,33869160 %N A187631 Number of (n+1)X(n+1) 0..3 arrays with the array of 2X2 subblock determinants antisymmetric under horizontal and vertical reflection and each non-centerline 2X2 subblock nonsingular. %C A187631 Column 3 of A187633 %e A187631 Some solutions for 4X4 %e A187631 ..1..2..3..1....0..2..1..2....3..2..2..2....1..1..3..0....1..2..2..3 %e A187631 ..3..0..0..2....1..0..0..2....3..0..0..3....3..0..0..1....1..0..0..1 %e A187631 ..3..0..0..2....2..0..0..2....2..0..0..2....1..0..0..1....2..0..0..1 %e A187631 ..0..2..3..3....2..1..1..3....2..3..3..1....2..3..3..1....0..1..2..2 %K A187631 nonn %O A187631 1,1 %A A187631 _R. H. Hardin_ Mar 12 2011