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A191293
Number of n X n symmetric binary matrices with each 1 adjacent to exactly 2 horizontally or vertically neighboring 1s
1
1, 2, 4, 13, 53, 278, 1915, 17298, 206161, 3270381, 68710560, 1908681423, 70045542183, 3395385492725, 217427456813709, 18398892775456083, 2057817979125478159, 304212919428910114290, 59440186835670090471326
OFFSET
1,2
LINKS
EXAMPLE
Some solutions for n=4
..1..1..1..1....1..1..0..0....0..0..0..0....1..1..1..0....1..1..1..0
..1..0..0..1....1..1..0..0....0..0..0..0....1..0..1..0....1..0..1..1
..1..0..1..1....0..0..1..1....0..0..1..1....1..1..1..0....1..1..0..1
..1..1..1..0....0..0..1..1....0..0..1..1....0..0..0..0....0..1..1..1
CROSSREFS
Sequence in context: A129091 A030970 A030842 * A151802 A030901 A030939
KEYWORD
nonn
AUTHOR
R. H. Hardin May 29 2011
STATUS
approved