A067209 Number of n X n 0..1 matrices with all row and column sums equal.

1, 2, 4, 14, 140, 4322, 434542, 144109562, 165431317452, 654143160457922, 9331115832294448754, 469229841129645179004962, 87481268294773501231007850158, 58328998963405322376273800187396962, 147013017541698957281403494604070439260442

Offset

0,2

Links

Alois P. Heinz, Table of n, a(n) for n = 0..30

E. R. Canfield and B. D. McKay, Asymptotic enumeration of dense 0-1 matrices with equal row and column sums

B. D. McKay, 0-1 matrices with constant row and column sums

Example

Some solutions for n=5
..1..1..0..0..1....0..0..1..0..1....0..1..0..1..1....1..1..0..1..0
..1..1..0..0..1....1..1..0..0..0....1..1..0..0..1....1..0..1..1..0
..0..0..1..1..1....1..0..0..1..0....1..1..1..0..0....1..0..1..0..1
..1..0..1..1..0....0..1..1..0..0....0..0..1..1..1....0..1..0..1..1
..0..1..1..1..0....0..0..0..1..1....1..0..1..1..0....0..1..1..0..1

Crossrefs

Row sums of A008300.

Column k=1 of A202784.

Sequence in context: A102897 A305856 A001527 * A134040 A368017 A061291

Adjacent sequences: A067206 A067207 A067208 * A067210 A067211 A067212

Keyword

nonn

Author

R. H. Hardin, Feb 20 2002

Extensions

Added one term and example - R. H. Hardin, Jan 05, 2012

a(0)=1 prepended and more terms (using data provided by B. D. McKay) from Alois P. Heinz, Apr 12 2017

Status

approved