A212130 Number of n X n binary matrices with zero diagonal and no directed 3-loops (3-loop: x(i,j)*x(j,k)*x(k,i)=1, and i,j,k all different)

1, 4, 49, 1699, 156532, 36686047, 21135750421

Offset

1,2

Links

Table of n, a(n) for n=1..7.

Example

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

Crossrefs

Sequence in context: A336805 A029991 A129419 * A049503 A159593 A263441

Adjacent sequences: A212127 A212128 A212129 * A212131 A212132 A212133

Keyword

nonn

Author

R. H. Hardin Jun 13 2012

Status

approved