A191293 Number of n X n symmetric binary matrices with each 1 adjacent to exactly 2 horizontally or vertically neighboring 1s

1, 2, 4, 13, 53, 278, 1915, 17298, 206161, 3270381, 68710560, 1908681423, 70045542183, 3395385492725, 217427456813709, 18398892775456083, 2057817979125478159, 304212919428910114290, 59440186835670090471326

Offset

1,2

Links

R. H. Hardin, Table of n, a(n) for n = 1..22

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

Adjacent sequences: A191290 A191291 A191292 * A191294 A191295 A191296

Keyword

nonn

Author

R. H. Hardin May 29 2011

Status

approved