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Number of n X n symmetric binary matrices with each 1 adjacent to no more than 1 E, SE or S neighboring 1
1

%I #6 Dec 18 2015 18:17:40

%S 2,6,32,294,4640,125338,5802288,459958324,62453890000,14523496866976,

%T 5784570667981520,3945961499388113436,4610186764537663968556,

%U 9225021921428355206788506,31615478219055162849230486428

%N Number of n X n symmetric binary matrices with each 1 adjacent to no more than 1 E, SE or S neighboring 1

%H R. H. Hardin, <a href="/A191691/b191691.txt">Table of n, a(n) for n = 1..24</a>

%e Some solutions for n=5

%e ..0..1..0..0..1....0..0..0..1..0....1..0..1..0..0....1..0..1..0..1

%e ..1..1..0..0..1....0..1..0..0..1....0..0..0..1..0....0..0..1..0..1

%e ..0..0..0..0..1....0..0..1..0..0....1..0..0..0..0....1..1..0..0..0

%e ..0..0..0..0..0....1..0..0..0..0....0..1..0..0..1....0..0..0..1..0

%e ..1..1..1..0..0....0..1..0..0..1....0..0..0..1..0....1..1..0..0..0

%K nonn

%O 1,1

%A _R. H. Hardin_ Jun 11 2011