A188400 Number of (6*n) X 6 binary arrays with rows in nonincreasing order, n ones in every column and no more than 2 ones in any row.

1, 76, 2578, 44288, 478711, 3710272, 22393101, 111200600, 472211360, 1763603560, 5916521021, 18121655192, 51328536740, 135834620472, 338676787932, 801091475448, 1808025242415, 3912600581712, 8152010122276, 16411466716600, 32022153082291, 60720959942432, 112158519503545

Offset

0,2

Comments

Number of 6 X 6 symmetric matrices with nonnegative integer entries and all row and column sums n. - Andrew Howroyd, Apr 07 2020

Links

Andrew Howroyd, Table of n, a(n) for n = 0..50

Example

Some solutions for 12X6
..1..0..0..1..0..0....1..0..0..0..1..0....1..0..0..1..0..0....1..1..0..0..0..0
..1..0..0..0..0..0....1..0..0..0..0..0....1..0..0..0..0..0....1..0..1..0..0..0
..0..1..0..0..0..0....0..1..1..0..0..0....0..1..1..0..0..0....0..1..1..0..0..0
..0..1..0..0..0..0....0..1..0..0..0..0....0..1..1..0..0..0....0..0..0..1..0..1
..0..0..1..1..0..0....0..0..1..1..0..0....0..0..0..1..0..0....0..0..0..1..0..1
..0..0..1..0..0..0....0..0..0..1..0..0....0..0..0..0..1..1....0..0..0..0..1..0
..0..0..0..0..1..1....0..0..0..0..1..0....0..0..0..0..1..0....0..0..0..0..1..0
..0..0..0..0..1..1....0..0..0..0..0..1....0..0..0..0..0..1....0..0..0..0..0..0
..0..0..0..0..0..0....0..0..0..0..0..1....0..0..0..0..0..0....0..0..0..0..0..0
..0..0..0..0..0..0....0..0..0..0..0..0....0..0..0..0..0..0....0..0..0..0..0..0
..0..0..0..0..0..0....0..0..0..0..0..0....0..0..0..0..0..0....0..0..0..0..0..0
..0..0..0..0..0..0....0..0..0..0..0..0....0..0..0..0..0..0....0..0..0..0..0..0

Crossrefs

Column 6 of A188403.

Sequence in context: A278092 A153177 A166191 * A205918 A261574 A017792

Adjacent sequences: A188397 A188398 A188399 * A188401 A188402 A188403

Keyword

nonn

Author

R. H. Hardin, Mar 30 2011

Extensions

a(0)=1 prepended and terms a(17) and beyond from Andrew Howroyd, Apr 07 2020

Status

approved