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%I #5 Dec 18 2015 18:18:08
%S 1,9,324,36801,13804290,17121995676,70150653652257,949536762106019733,
%T 42462806002512959389608,6273638029264294190600689986
%N 1/4 the number of n X n 0..3 symmetric matrices with every element equal to zero, one or three horizontal and vertical neighbors
%e Some solutions for n=4
%e ..0..3..2..3....1..2..0..0....0..3..2..2....1..3..3..0....1..0..3..2
%e ..3..1..2..0....2..0..2..1....3..0..1..0....3..0..1..3....0..2..3..0
%e ..2..2..3..2....0..2..0..3....2..1..3..0....3..1..3..1....3..3..1..0
%e ..3..0..2..3....0..1..3..1....2..0..0..1....0..3..1..2....2..0..0..3
%K nonn
%O 1,2
%A _R. H. Hardin_ Mar 31 2012
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