A213793 Number of n X n 0..1 symmetric arrays with every row summing to floor(n/2).

1, 1, 2, 4, 18, 112, 1760, 35150, 1944530, 133948836, 26615510712, 6549149852112, 4762109992158288, 4274712091685443584, 11528251571501588791296, 38295413179145036856212700, 386860001875783390762182911250, 4805622573099374975572752075805000

Offset: 0

Author

R. H. Hardin, Jun 20 2012

Keywords

• nonn

Examples

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

Links

• Andrew Howroyd, Table of n, a(n) for n = 0..24

Crossrefs

Column 1 of A213800.

Cf. A333164.

Formula

a(2*n) = A333164(n). - Andrew Howroyd, Apr 08 2020

Extensions

a(0)=1 prepended and terms a(13) and beyond from Andrew Howroyd, Apr 08 2020