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%I #6 Dec 18 2015 18:18:06
%S 1,4,40,800,33432,2888696,517902680,192533704008,148429379845856,
%T 237284500891487840,786611979025079107456,5407447771030956200932952,
%U 77084070831919712319047890192,2278648745820732735808198902023640
%N 1/3 the number of n X n 0..2 symmetric matrices with every element equal to zero or one horizontal or vertical neighbor
%e Some solutions for n=4
%e ..1..0..2..2....2..1..0..0....0..1..0..2....0..1..1..0....1..2..1..0
%e ..0..1..0..0....1..0..2..1....1..2..0..2....1..2..0..2....2..0..1..2
%e ..2..0..1..2....0..2..0..2....0..0..2..0....1..0..2..0....1..1..0..1
%e ..2..0..2..1....0..1..2..0....2..2..0..1....0..2..0..1....0..2..1..0
%K nonn
%O 1,2
%A _R. H. Hardin_ Mar 30 2012
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