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%I #6 Dec 18 2015 18:18:07
%S 1,16,936,210780,181263453,596226368451,7500390386674716,
%T 360860802332072507724,66401649279259441073029473,
%U 46730621582712339208520777565573
%N 1/4 the number of n X n 0..3 symmetric matrices with every element equal to zero, one or two horizontal and vertical neighbors
%H R. H. Hardin, <a href="/A211081/b211081.txt">Table of n, a(n) for n = 1..11</a>
%e Some solutions for n=4
%e ..0..2..1..3....2..2..3..3....2..2..3..3....2..0..1..2....2..0..3..2
%e ..2..0..0..2....2..0..2..1....2..0..3..3....0..0..2..3....0..2..1..0
%e ..1..0..0..1....3..2..1..3....3..3..2..1....1..2..1..1....3..1..3..2
%e ..3..2..1..0....3..1..3..1....3..3..1..3....2..3..1..0....2..0..2..3
%K nonn
%O 1,2
%A _R. H. Hardin_ Mar 31 2012
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