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%I #6 Dec 18 2015 18:17:40
%S 2,8,52,686,16484,740480,62224406,9743390402,2847964953844,
%T 1553270286186274,1580697070071238528,3001650015211411938494,
%U 10635826342196669611219640,70320933672952732438772180006
%N Number of n X n symmetric binary matrices with each 1 adjacent to no more than 3 horizontally, vertically or diagonally neighboring 1s
%H R. H. Hardin, <a href="/A191602/b191602.txt">Table of n, a(n) for n = 1..16</a>
%e Some solutions for n=4
%e ..1..1..0..1....0..0..0..1....0..1..1..0....0..0..1..1....1..0..0..0
%e ..1..1..0..1....0..0..0..1....1..0..1..0....0..1..0..1....0..1..0..1
%e ..0..0..0..0....0..0..0..1....1..1..0..0....1..0..0..1....0..0..1..0
%e ..1..1..0..0....1..1..1..0....0..0..0..0....1..1..1..1....0..1..0..1
%K nonn
%O 1,1
%A _R. H. Hardin_ Jun 08 2011
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