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

Author

N. J. A. Sloane, Jul 13 2003

Keywords

• nonn

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.

Examples

			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.
		

Links

• Index entries for sequences related to binary matrices

Crossrefs

Cf. A084553, A085659, A080858, A083029.

Extensions

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