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 A187520 #6 Jul 22 2025 10:47:42 %S A187520 170,3426,107990,8174314,1201064094 %N A187520 Number of (n+1)X(n+1) 0..5 arrays with the array of 2X2 subblock determinants antisymmetric and no off-diagonal 2X2 subblock determinant zero. %C A187520 Column 5 of A187521 %e A187520 Some solutions for 4X4 %e A187520 ..0..0..3..2....0..5..1..1....0..0..2..0....0..0..3..0....2..2..3..1 %e A187520 ..3..2..1..2....0..5..5..1....3..4..1..1....3..5..3..5....1..1..2..2 %e A187520 ..0..2..1..3....4..3..3..3....1..4..1..3....0..5..3..4....2..1..2..1 %e A187520 ..2..1..0..0....4..4..0..0....1..2..0..0....3..4..3..4....4..0..2..1 %K A187520 nonn %O A187520 1,1 %A A187520 _R. H. Hardin_ Mar 10 2011