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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.

A187531 Number of 5X5 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 A187531 #6 Jul 22 2025 10:48:55
%S A187531 0,1476,20554,273102,992410,5880944
%N A187531 Number of 5X5 0..n arrays with each 2X2 subblock determinant nonzero and the array of 2X2 subblock determinants symmetric under 90 degree rotation.
%C A187531 Row 4 of A187528
%e A187531 Some solutions for 5X5
%e A187531 ..2..3..3..0..3....3..3..1..0..1....2..0..2..1..3....0..2..1..0..1
%e A187531 ..3..0..1..3..0....1..0..1..3..1....1..1..1..0..2....1..0..1..2..0
%e A187531 ..2..3..2..3..1....3..3..2..3..2....2..1..2..1..2....1..2..2..2..1
%e A187531 ..1..3..1..0..3....2..3..1..0..1....2..0..1..1..1....0..2..1..0..1
%e A187531 ..3..0..3..3..1....1..0..1..3..3....1..1..2..0..2....1..2..2..2..2
%K A187531 nonn
%O A187531 1,2
%A A187531 _R. H. Hardin_ Mar 10 2011

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