1,2
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.
Index entries for sequences related to binary matrices
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.
Cf. A084553, A085659, A080858, A083029.
Sequence in context: A088792 A114160 A145159 * A094664 A001858 A000366
Adjacent sequences: A084549 A084550 A084551 * A084553 A084554 A084555
nonn
N. J. A. Sloane (njas(AT)research.att.com), Jul 13 2003
a(6)-a(10) from Max Alekseyev, Jan 16 2006
