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%I #6 Dec 18 2015 18:17:39
%S 1,1,2,3,8,35,208,1147,10098,106904,1615656,31267328,833655362,
%T 29769092579,1422289731681,88322500448612,7254260374065120,
%U 782791757341222545,111845565903325791194,21080332457396845047136
%N Number of n X n symmetric binary matrices with each 1 adjacent to exactly 2 diagonally or antidiagonally neighboring 1s
%H R. H. Hardin, <a href="/A191274/b191274.txt">Table of n, a(n) for n = 1..22</a>
%e All solutions for n=4
%e ..0..0..0..0....0..1..0..0....0..0..0..0
%e ..0..0..1..0....1..0..1..0....0..0..0..0
%e ..0..1..0..1....0..1..0..0....0..0..0..0
%e ..0..0..1..0....0..0..0..0....0..0..0..0
%K nonn
%O 1,3
%A _R. H. Hardin_ May 29 2011
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