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 A187526 #6 Jul 22 2025 10:48:19 %S A187526 50,8,3790,1476,3607148,296232 %N A187526 Number of (n+1)X(n+1) 0..2 arrays with each 2X2 subblock determinant nonzero and the array of 2X2 subblock determinants symmetric under 90 degree rotation. %C A187526 Column 2 of A187528 %e A187526 Some solutions for 4X4 %e A187526 ..2..1..0..1....2..0..2..0....1..0..1..0....2..2..0..2....2..2..2..2 %e A187526 ..1..0..1..2....0..1..0..1....0..1..0..1....2..1..1..2....1..0..1..0 %e A187526 ..1..1..0..1....2..2..2..2....1..2..1..2....2..2..0..2....2..2..0..2 %e A187526 ..1..0..1..0....1..2..1..2....0..1..0..1....2..1..1..2....2..1..1..0 %K A187526 nonn %O A187526 1,1 %A A187526 _R. H. Hardin_ Mar 10 2011