A084552 Number of n X n symmetric positive definite matrices with 2's on the main diagonal and -1's and 0's elsewhere.

1, 2, 7, 38, 286, 2686, 28512, 312572, 3337588, 40963216

Offset

1,2

Comments

Of course the total number of symmetric matrices of this type (not necessarily positive definite) is 2^C(n,2).

This gives the number of different values of M + M' where M runs through the matrices counted in A127502.

Links

Table of n, a(n) for n=1..10.

Index entries for sequences related to binary matrices

Example

The singular matrix
2 -1 -1
-1 2 -1
-1 -1 2
is the only 3 X 3 matrix of this type which is not positive definite.

Crossrefs

Cf. A084553, A085659, A080858, A083029.

Sequence in context: A114160 A145159 A317985 * A094664 A001858 A233335

Adjacent sequences: A084549 A084550 A084551 * A084553 A084554 A084555

Keyword

nonn

Author

N. J. A. Sloane, Jul 13 2003

Extensions

a(6)-a(10) from Max Alekseyev, Jan 16 2006

Status

approved