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A210920 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 0

%I

%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

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Last modified January 29 20:26 EST 2023. Contains 359926 sequences. (Running on oeis4.)