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%I #5 Dec 18 2015 18:18:07
%S 0,1,0,12,18,624,6012,228984,8210664,619049280,63783422784,
%T 11382530540616
%N 1/4 the number of n X n 0..3 symmetric matrices with every element equal to two or three horizontal and vertical neighbors
%e Some solutions for n=6
%e ..1..1..1..1..1..1....2..2..1..1..0..0....2..2..0..0..1..1....0..0..3..3..1..1
%e ..1..3..3..1..1..1....2..2..1..1..0..0....2..2..0..0..1..1....0..0..3..3..1..1
%e ..1..3..3..1..2..2....1..1..2..2..3..3....0..0..1..1..2..2....3..3..2..2..1..1
%e ..1..1..1..1..2..2....1..1..2..2..3..3....0..0..1..1..2..2....3..3..2..2..1..1
%e ..1..1..2..2..0..0....0..0..3..3..2..2....1..1..2..2..0..0....1..1..1..1..2..2
%e ..1..1..2..2..0..0....0..0..3..3..2..2....1..1..2..2..0..0....1..1..1..1..2..2
%K nonn
%O 1,4
%A _R. H. Hardin_ Mar 31 2012
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