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%I #5 Dec 18 2015 18:18:06
%S 0,1,4,72,2088,148758,21763840,7132571384,5048293367644,
%T 7844581606488974,26582841246234004080,197025807090354544802766
%N 1/3 the number of n X n 0..2 symmetric matrices with every element equal to one or two horizontal and vertical neighbors
%e Some solutions for n=4
%e ..0..0..2..2....0..0..2..2....2..2..1..1....0..0..0..0....2..2..2..2
%e ..0..1..1..2....0..1..1..1....2..2..1..2....0..1..1..0....2..0..0..1
%e ..2..1..0..0....2..1..0..0....1..1..1..2....0..1..2..2....2..0..0..1
%e ..2..2..0..0....2..1..0..0....1..2..2..2....0..0..2..2....2..1..1..1
%K nonn
%O 1,3
%A _R. H. Hardin_ Mar 30 2012