A191344 Number of n X n symmetric binary matrices with each 1 adjacent to exactly 2 horizontally, vertically or diagonally neighboring 1s

1, 1, 3, 11, 47, 294, 2274, 23217, 346865, 7054923, 194307949, 7369451741, 380583130482, 26850075718493, 2600396553939968, 344812336151621752, 62585126371789861439, 15557855832828751119291

Offset

1,3

Links

Table of n, a(n) for n=1..18.

Example

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

Crossrefs

Sequence in context: A111139 A167564 A295833 * A308538 A181278 A126180

Adjacent sequences: A191341 A191342 A191343 * A191345 A191346 A191347

Keyword

nonn

Author

R. H. Hardin May 30 2011

Status

approved