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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.

A187697 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 horizontal and vertical reflection.

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%I A187697 #6 Jul 22 2025 10:52:46
%S A187697 50,8,7954,1548,15128848,454640,231192094416
%N A187697 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 horizontal and vertical reflection.
%C A187697 Column 2 of A187699
%e A187697 Some solutions for 4X4
%e A187697 ..0..2..0..2....2..0..2..0....2..2..0..2....1..2..1..0....1..2..0..2
%e A187697 ..1..1..1..1....1..2..0..2....1..0..1..0....0..1..0..1....2..2..1..2
%e A187697 ..0..1..0..1....2..0..2..0....0..2..0..2....1..0..1..0....1..2..0..2
%e A187697 ..2..1..2..0....1..2..1..2....1..0..1..0....0..1..2..1....2..2..1..0
%K A187697 nonn
%O A187697 1,1
%A A187697 _R. H. Hardin_ Mar 12 2011

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