A027832 Number of symmetric {-1, +1} matrices of order n with nonnegative row and column sums.

1, 5, 14, 315, 2634, 301262, 8035168, 4451407563, 392447922178, 1028823851939030, 306635655405986312, 3743721825782942609558, 3832881704712490758507152, 215313862348697780762374273824, 766493362781127793638943080523776, 196222469681558506008588371784165178651, 2452358136558134202145977229121349160510450

Offset

1,2

References

I. Anderson, Combinatorics of Finite Sets, Oxford 1987, Ch. 3.1.

Torsten Sillke and Achim Flammenkamp, unpublished.

Links

Table of n, a(n) for n=1..17.

C. Greene and D. J. Kleitman, Strong versions of Sperner's Theorem, J. Combin. Theory, A 20 (1976) 80-88.

Example

n=2: A(2) = 5 from ++/++, ++/+-, -+/++, -+/+-, +-/-+

Crossrefs

Sequence in context: A317037 A317691 A067857 * A128946 A156219 A000331

Adjacent sequences: A027829 A027830 A027831 * A027833 A027834 A027835

Keyword

nonn,nice

Author

Torsten Sillke (sillke(AT)Mathematik.Uni-Bielefeld.DE)

Status

approved