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Number of n X n symmetric binary matrices containing no more than one 1 in any 2 X 2 sub-block.
1

%I #8 Mar 09 2015 04:27:38

%S 1,2,3,9,28,137,811,6884,75303,1133287,22573092,608722751,21933950111,

%T 1064082678978,69200610896639,6047740350081131,709281636920027844,

%U 111719166691840119209,23622672695690329752039

%N Number of n X n symmetric binary matrices containing no more than one 1 in any 2 X 2 sub-block.

%H R. H. Hardin, May 31 2008, <a href="/A139006/b139006.txt">Table of n, a(n) for n = 0..28</a>

%K nonn

%O 0,2

%A _R. H. Hardin_, May 31 2008