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 A187630 #6 Jul 22 2025 10:50:56 %S A187630 31,446,1648,557382,672698,21411605018,22329564088 %N A187630 Number of (n+1)X(n+1) 0..2 arrays with the array of 2X2 subblock determinants antisymmetric under horizontal and vertical reflection and each non-centerline 2X2 subblock nonsingular. %C A187630 Column 2 of A187633 %e A187630 Some solutions for 4X4 %e A187630 ..2..0..0..2....2..1..2..0....1..1..1..0....1..2..2..1....0..1..2..1 %e A187630 ..1..1..1..0....2..0..0..1....2..0..0..2....2..2..2..2....2..0..0..1 %e A187630 ..2..2..2..0....1..0..0..1....2..0..0..1....2..2..2..2....1..0..0..1 %e A187630 ..1..0..0..1....2..2..2..2....1..1..2..0....1..2..2..1....1..2..2..1 %K A187630 nonn %O A187630 1,1 %A A187630 _R. H. Hardin_ Mar 12 2011