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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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

R. H. Hardin, Table of n, a(n) for n = 1..21

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: A191552 A154828 A057629 * A191602 A145157 A323871

Adjacent sequences:  A191504 A191505 A191506 * A191508 A191509 A191510

KEYWORD

nonn

AUTHOR

R. H. Hardin Jun 04 2011

STATUS

approved

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Last modified January 22 07:30 EST 2020. Contains 331139 sequences. (Running on oeis4.)