A180978 Number of n X n binary matrices with floor(n^2/2) 1's and rows and columns in lexicographically nondecreasing order

1, 3, 10, 121, 3680, 326650, 91271990, 74872992399, 208579984612008, 1748923742658486631

Offset

1,2

Comments

Diagonal of A180979

Links

Table of n, a(n) for n=1..10.

Example

All solutions for 3X3
..0..0..0....0..0..0....0..0..0....0..0..1....0..0..1....0..0..1....0..0..1
..0..1..1....0..0..1....0..1..1....0..1..0....0..0..1....0..1..0....0..1..0
..0..1..1....1..1..1....1..0..1....0..1..1....0..1..1....1..1..0....1..0..1
...
..0..0..1....0..0..1....0..1..1
..0..0..1....0..1..1....1..0..0
..1..1..0....1..0..0....1..0..0

Crossrefs

Sequence in context: A336210 A244305 A074260 * A241461 A175079 A333430

Adjacent sequences: A180975 A180976 A180977 * A180979 A180980 A180981

Keyword

nonn

Author

R. H. Hardin Sep 30 2010

Status

approved