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 A187698 #6 Jul 22 2025 10:52:53 %S A187698 192,74,87258,22738,1089964504 %N A187698 Number of (n+1)X(n+1) 0..3 arrays with each 2X2 subblock determinant nonzero and the array of 2X2 subblock determinants symmetric under horizontal and vertical reflection. %C A187698 Column 3 of A187699 %e A187698 Some solutions for 4X4 %e A187698 ..2..2..1..2....0..3..0..3....1..2..2..2....2..3..1..0....0..1..0..1 %e A187698 ..3..0..3..0....2..1..2..1....2..0..2..0....1..3..0..3....3..1..3..1 %e A187698 ..2..2..0..2....0..2..0..2....2..2..0..2....2..3..1..2....3..2..3..2 %e A187698 ..3..0..3..2....3..2..3..3....2..0..2..1....1..3..0..3....3..1..3..1 %K A187698 nonn %O A187698 1,1 %A A187698 _R. H. Hardin_ Mar 12 2011