A188405 Number of (4*n) X n binary arrays with rows in nonincreasing order, 4 ones in every column and no more than 2 ones in any row.

1, 1, 5, 42, 641, 14751, 478711, 20758650, 1158207312, 80758709676, 6877184737416, 701994697409136, 84574042067524470, 11870290445670605262, 1919446717950100963626, 354168049679464581788796, 73947210994621695613727526, 17342441149450781813176059990

Offset: 0

Author

R. H. Hardin, Mar 30 2011

Keywords

• nonn

Comments

Number of n X n symmetric matrices with nonnegative integer entries and all row and column sums 4. - Andrew Howroyd, Apr 07 2020

In A005816 matrix elements on the diagonal are counted with a factor 2. This sequence here counts labeled multigraphs with n nodes (may be disconnected, undirected edges) without loops and degree at each node <=4. - R. J. Mathar, Jun 05 2022

Examples

			All solutions for 8X2
..1..1....1..1....1..1....1..0....1..1
..1..0....1..1....1..1....1..0....1..1
..1..0....1..1....1..0....1..0....1..1
..1..0....1..0....1..0....1..0....1..1
..0..1....0..1....0..1....0..1....0..0
..0..1....0..0....0..1....0..1....0..0
..0..1....0..0....0..0....0..1....0..0
..0..0....0..0....0..0....0..1....0..0
		

Links

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

Crossrefs

Row 4 of A188403.

Cf. A139670 (matrix elements 0 or 1).

Extensions

a(0)=1 prepended and terms a(12) and beyond from Andrew Howroyd, Apr 07 2020