id:A084552 - OEIS Search Results

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

+0
3

1, 2, 7, 38, 286, 2686, 28512, 312572, 3337588, 40963216 (list; graph; listen)

	OFFSET	`1,2`
	COMMENT	`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	`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.` `Adjacent sequences: A084549 A084550 A084551 this_sequence A084553 A084554 A084555` `Sequence in context: A032109 A088792 A114160 this_sequence A094664 A001858 A000366`
	KEYWORD	`nonn`
	AUTHOR	`njas, Jul 13 2003`
	EXTENSIONS	`a(6)-a(10) from Max Alekseyev, Jan 16 2006`

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Last modified October 15 09:18 EDT 2008. Contains 145015 sequences.