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%I #5 Dec 18 2015 18:18:07
%S 1,4,48,1104,54408,5624336,1223018480,559805180336,539124008193384,
%T 1092375543732930912,4656812532055124194440,41767144321757757477117792
%N 1/3 the number of n X n 0..2 symmetric matrices with every element equal to zero or one horizontal and vertical neighbors
%e Some solutions for n=4
%e ..2..1..2..2....1..0..2..0....1..2..1..2....1..0..1..2....2..0..2..1
%e ..1..0..1..0....0..2..1..2....2..0..1..0....0..2..0..0....0..2..0..1
%e ..2..1..0..1....2..1..1..1....1..1..2..0....1..0..2..1....2..0..1..0
%e ..2..0..1..2....0..2..1..2....2..0..0..2....2..0..1..2....1..1..0..2
%K nonn
%O 1,2
%A _R. H. Hardin_ Mar 30 2012