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%I #7 Dec 18 2015 18:17:40
%S 2,5,23,159,1646,28059,724310,29626607,1890041732,188477431884,
%T 29421793928187,7179932235630885,2740816166752070599,
%U 1636347059803667113339,1527949588062203773106011
%N Number of n X n symmetric binary matrices with each 1 adjacent to no more than 1 horizontally, vertically or diagonally neighboring 1
%H R. H. Hardin, <a href="/A191600/b191600.txt">Table of n, a(n) for n = 1..20</a>
%e Some solutions for n=4
%e ..0..1..0..0....0..0..1..1....1..0..0..1....0..0..1..0....1..0..1..1
%e ..1..0..0..0....0..0..0..0....0..0..0..0....0..0..0..0....0..0..0..0
%e ..0..0..1..0....1..0..1..0....0..0..1..0....1..0..1..0....1..0..0..0
%e ..0..0..0..1....1..0..0..1....1..0..0..0....0..0..0..1....1..0..0..1
%K nonn
%O 1,1
%A _R. H. Hardin_ Jun 08 2011