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A085658 Number of n X n symmetric positive semi-definite matrices with 2's on the main diagonal and 1's and 0's elsewhere. 6
1, 2, 8, 64, 924, 21737, 749684, 33568376 (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 semi-definite) is 2^C(n,2).
This gives the number of different values of M + M' where M runs through the matrices counted in A038379. - Max Alekseyev, Nov 11 2006
LINKS
EXAMPLE
The matrix
2 0 0 0 1
0 2 0 1 1
0 0 2 1 1
0 1 1 2 0
1 1 1 0 2
is one of the 100 5 X 5 matrices which are not positive semi-definite.
Its eigenvalues are approximately [2., -0.135779205069857, 4.135779205069857, 1.337846553138044, 2.662153446861956]
CROSSREFS
Sequence in context: A134956 A011803 A007625 * A153541 A153569 A153532
KEYWORD
nonn,more
AUTHOR
N. J. A. Sloane, Jul 12 2003
EXTENSIONS
3 more terms from Max Alekseyev, Nov 08 2006
STATUS
approved

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Last modified March 19 06:29 EDT 2024. Contains 370953 sequences. (Running on oeis4.)