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%I #5 Dec 18 2015 18:18:07
%S 1,9,297,31671,11073510,12788362323,48662429782212,610280363553528555,
%T 25226141633402684949288,3436779288522895580112954426,
%U 1543230902313982340399083345635951
%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 ..1..0..0..1....2..0..0..0....1..2..3..3....1..3..3..2....0..2..2..3
%e ..0..1..2..2....0..1..0..1....2..3..2..0....3..2..1..0....2..1..0..1
%e ..0..2..0..3....0..0..1..0....3..2..3..2....3..1..0..3....2..0..3..1
%e ..1..2..3..1....0..1..0..1....3..0..2..0....2..0..3..2....3..1..1..2
%K nonn
%O 1,2
%A _R. H. Hardin_ Mar 31 2012
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