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 A187623 #6 Jul 22 2025 10:50:13 %S A187623 64,2924,390,12278892,4232368 %N A187623 Number of (n+1)X(n+1) 0..3 arrays with each 2X2 non-center subblock determinant nonzero and the array of 2X2 subblock determinants antisymmetric under 90 degree rotation. %C A187623 Column 3 of A187624 %e A187623 Some solutions for 4X4 %e A187623 ..1..0..2..3....1..1..0..1....1..3..2..3....2..1..0..2....1..2..1..2 %e A187623 ..3..1..1..1....0..1..1..1....0..1..1..1....0..1..1..2....0..1..1..1 %e A187623 ..1..1..1..3....1..1..1..0....1..1..1..0....1..1..1..1....1..1..1..0 %e A187623 ..3..2..0..1....2..1..2..1....3..2..3..1....2..0..1..3....2..1..2..1 %K A187623 nonn %O A187623 1,1 %A A187623 _R. H. Hardin_ Mar 12 2011