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%I #5 Dec 18 2015 18:18:07
%S 1,10,228,13227,1888962,662705112,570731832303,1205311139476404,
%T 6235576486183465116,78976030794422736761688
%N 1/4 the number of n X n 0..3 symmetric matrices with every element equal to zero, two or three horizontal and vertical neighbors
%e Some solutions for n=4
%e ..0..3..1..3....2..1..2..1....0..1..0..3....0..2..3..0....0..2..3..1
%e ..3..1..3..1....1..2..3..0....1..0..1..2....2..0..2..3....2..0..2..3
%e ..1..3..1..0....2..3..2..1....0..1..3..1....3..2..3..1....3..2..1..0
%e ..3..1..0..2....1..0..1..0....3..2..1..0....0..3..1..0....1..3..0..1
%K nonn
%O 1,2
%A _R. H. Hardin_ Mar 31 2012
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