A191508 Number of n X n symmetric binary matrices with each 1 adjacent to no more than 3 horizontally or vertically neighboring 1's.

2, 8, 56, 792, 21984, 1188160, 125522112, 25932064896, 10472077118464, 8266074697979136, 12754433913314441216, 38469498012053658897408, 226810241439860068417249280, 2613967215944945112514234085376

Offset

1,1

Links

R. H. Hardin, Table of n, a(n) for n = 1..25

Example

Some solutions for n=4
..0..1..0..0....0..0..1..1....0..0..0..1....0..0..0..1....1..0..0..0
..1..0..1..0....0..0..0..1....0..0..0..1....0..1..1..1....0..0..1..0
..0..1..0..1....1..0..0..0....0..0..0..1....0..1..1..0....0..1..0..0
..0..0..1..1....1..1..0..1....1..1..1..0....1..1..0..1....0..0..0..0

Crossrefs

Sequence in context: A084872 A254231 A191713 * A113725 A345677 A256724

Adjacent sequences: A191505 A191506 A191507 * A191509 A191510 A191511

Keyword

nonn

Author

R. H. Hardin, Jun 04 2011

Status

approved