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A191507
Number of n X n symmetric binary matrices with each 1 adjacent to no more than 2 horizontally or vertically neighboring 1s
1
2, 8, 52, 646, 14570, 599702, 45191945, 6225542127, 1567856872728, 722008623925586, 607932060252871024, 935917819388424802645, 2634499346573878930718088, 13559220442178025486399949918
OFFSET
1,1
LINKS
EXAMPLE
Some solutions for n=4
..1..0..0..1....0..1..0..1....1..1..0..0....0..0..1..0....1..0..1..0
..0..1..1..1....1..1..0..0....1..1..0..1....0..0..0..0....0..0..1..1
..0..1..0..0....0..0..0..0....0..0..0..0....1..0..0..1....1..1..0..1
..1..1..0..0....1..0..0..0....0..1..0..1....0..0..1..0....0..1..1..0
CROSSREFS
Sequence in context: A154828 A349012 A057629 * A191602 A145157 A323871
KEYWORD
nonn
AUTHOR
R. H. Hardin Jun 04 2011
STATUS
approved