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Number of n X n symmetric binary matrices with each 1 adjacent to exactly 2 knight-move neighboring 1s
0

%I #5 Dec 18 2015 18:17:39

%S 1,1,2,17,61,241,1077,10002,130992,2166639,41299118,1000354787,

%T 34454184106

%N Number of n X n symmetric binary matrices with each 1 adjacent to exactly 2 knight-move neighboring 1s

%e Some solutions for n=4

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

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

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

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

%K nonn

%O 1,3

%A _R. H. Hardin_ May 29 2011