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%I #7 Dec 18 2015 18:18:07
%S 1,9,297,30213,9904329,10357083063,34636341072699,370225462363917579,
%T 12650055630492583306593,1381655999590131944779825905,
%U 482381759955085135355798493794163
%N 1/4 the number of n X n 0..3 symmetric matrices with every element equal to zero or one horizontal and vertical neighbors
%H R. H. Hardin, <a href="/A211077/b211077.txt">Table of n, a(n) for n = 1..12</a>
%e Some solutions for n=4
%e ..0..3..2..3....0..1..2..1....1..0..2..2....3..0..1..0....2..3..0..3
%e ..3..1..0..1....1..3..0..1....0..1..3..1....0..2..1..3....3..2..1..1
%e ..2..0..2..0....2..0..2..3....2..3..0..1....1..1..3..2....0..1..3..0
%e ..3..1..0..1....1..1..3..0....2..1..1..2....0..3..2..0....3..1..0..1
%K nonn
%O 1,2
%A _R. H. Hardin_ Mar 31 2012
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