A127503 Number of n X n matrices A with 1's on the main diagonal and -1's and 0's elsewhere such that A + A' has only 0's and -1's off the main diagonal and is positive semi-definite.

1, 3, 27, 281, 3945, 70635, 1437555, 30357425, 628337745

Offset

1,2

Comments

For number of different values of A + A' see A084553.

Links

Table of n, a(n) for n=1..9.

Crossrefs

Cf. A085657, A085658, A080858, A083029, A038379, A127502.

Sequence in context: A098401 A355363 A011544 * A214363 A377238 A204821

Adjacent sequences: A127500 A127501 A127502 * A127504 A127505 A127506

Keyword

nonn,more,nice

Author

Max Alekseyev, Jan 16 2007

Status

approved