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.
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
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Jul 13 2003
EXTENSIONS
a(6)-a(10) from Max Alekseyev, Jan 16 2006
STATUS
approved