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A084552 Number of n X n symmetric positive definite matrices with 2's on the main diagonal and -1's and 0's elsewhere. 2
1, 2, 7, 38, 286, 2686, 28512, 312572, 3337588, 40963216 (list; graph; refs; listen; history; text; internal format)
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
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
Sequence in context: A114160 A145159 A317985 * A094664 A001858 A233335
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Jul 13 2003
EXTENSIONS
a(6)-a(10) from Max Alekseyev, Jan 16 2006
STATUS
approved

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Last modified March 18 22:56 EDT 2024. Contains 370952 sequences. (Running on oeis4.)