%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.
%A _N. J. A. Sloane_, Jul 13 2003
%E a(6)-a(10) from _Max Alekseyev_, Jan 16 2006