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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.

A187530 Number of 4X4 0..n arrays with each 2X2 subblock determinant nonzero and the array of 2X2 subblock determinants symmetric under 90 degree rotation.

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%I A187530 #6 Jul 22 2025 10:48:48
%S A187530 104,3790,35026,220802,727842,2327574,5366230,13768228,28531154,
%T A187530 54987216,90945478
%N A187530 Number of 4X4 0..n arrays with each 2X2 subblock determinant nonzero and the array of 2X2 subblock determinants symmetric under 90 degree rotation.
%C A187530 Row 3 of A187528
%e A187530 Some solutions for 4X4
%e A187530 ..3..1..2..1....3..3..1..3....3..0..3..1....2..3..3..3....2..1..0..1
%e A187530 ..1..0..1..0....2..3..0..3....1..2..0..2....1..0..1..0....2..0..2..1
%e A187530 ..0..1..0..1....1..0..1..0....3..0..3..3....3..3..0..3....0..1..0..1
%e A187530 ..1..0..1..0....0..3..0..3....0..2..0..2....1..0..1..2....2..3..2..2
%K A187530 nonn
%O A187530 1,1
%A A187530 _R. H. Hardin_ Mar 10 2011

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