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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

%I

%S 1,2,7,38,286,2686,28512,312572,3337588,40963216

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

%C Of course the total number of symmetric matrices of this type (not necessarily positive definite) is 2^C(n,2).

%C This gives the number of different values of M + M' where M runs through the matrices counted in A127502.

%H <a href="/index/Mat#binmat">Index entries for sequences related to binary matrices</a>

%e The singular matrix

%e 2 -1 -1

%e -1 2 -1

%e -1 -1 2

%e is the only 3 X 3 matrix of this type which is not positive definite.

%Y Cf. A084553, A085659, A080858, A083029.

%K nonn

%O 1,2

%A _N. J. A. Sloane_, Jul 13 2003

%E a(6)-a(10) from _Max Alekseyev_, Jan 16 2006

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Last modified March 18 16:00 EDT 2019. Contains 321292 sequences. (Running on oeis4.)