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Number of (2n)X(2n) 0..3 symmetric matrices with every element equal to two horizontal and vertical neighbors, and new values 0..3 introduced in lower triangle row major order
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%I #4 Mar 31 2012 12:37:34

%S 1,3,70,6516,1741480,1297416720,2686765690144,15449867954722880

%N Number of (2n)X(2n) 0..3 symmetric matrices with every element equal to two horizontal and vertical neighbors, and new values 0..3 introduced in lower triangle row major order

%e All solutions for n=2

%e ..0..0..1..1....0..0..1..1....0..0..0..0

%e ..0..0..1..1....0..0..1..1....0..1..1..0

%e ..1..1..2..2....1..1..0..0....0..1..1..0

%e ..1..1..2..2....1..1..0..0....0..0..0..0

%K nonn

%O 1,2

%A _R. H. Hardin_ Mar 29 2012