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 A187702 #6 Apr 21 2021 14:18:40 %S A187702 64,8272,322,81456,530,230446 %N A187702 Number of (n+1) X (n+1) 0..3 arrays with each 2 X 2 subblock off diagonal and antidiagonal nonsingular and the array of 2 X 2 subblock determinants antisymmetric about the diagonal and antidiagonal. %C A187702 Column 3 of A187705. %e A187702 Some solutions for 4 X 4 %e A187702 ..0..0..3..0....0..0..2..0....2..1..0..0....0..0..1..1....0..2..0..0 %e A187702 ..2..1..1..0....2..3..2..0....2..1..1..1....3..3..3..3....0..1..1..2 %e A187702 ..3..3..3..3....0..3..2..3....3..1..1..0....0..1..1..2....2..1..1..0 %e A187702 ..2..2..1..1....0..3..0..0....0..0..1..0....0..3..0..0....0..0..2..0 %Y A187702 Cf. A187705. %K A187702 nonn %O A187702 1,1 %A A187702 _R. H. Hardin_ Mar 12 2011