A191507 Number of n X n symmetric binary matrices with each 1 adjacent to no more than 2 horizontally or vertically neighboring 1s

2, 8, 52, 646, 14570, 599702, 45191945, 6225542127, 1567856872728, 722008623925586, 607932060252871024, 935917819388424802645, 2634499346573878930718088, 13559220442178025486399949918

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: A154828 A349012 A057629 * A378400 A191602 A145157

Adjacent sequences: A191504 A191505 A191506 * A191508 A191509 A191510

Keyword

nonn

Author

R. H. Hardin Jun 04 2011

Status

approved