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%I #7 Jun 20 2022 20:21:01
%S 1,9,204,12780,2172082,1005151346,1266392434410,4344083373089662,
%T 40572956283401922254,1031771738712216572967968,
%U 71439807978713378989930266486,13468111519258747911321811422788604
%N 1/3 the number of n X n 0..2 symmetric matrices with every element equal to zero, one or two horizontal and vertical neighbors.
%e Some solutions for n=4
%e ..1..1..2..1....2..0..1..0....1..2..0..1....2..0..0..2....1..2..0..1
%e ..1..1..2..1....0..2..2..2....2..2..1..2....0..2..0..0....2..1..0..2
%e ..2..2..0..1....1..2..0..1....0..1..1..2....0..0..2..2....0..0..1..1
%e ..1..1..1..1....0..2..1..1....1..2..2..2....2..0..2..2....1..2..1..2
%K nonn
%O 1,2
%A _R. H. Hardin_, Mar 30 2012
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