Let Q(z, w) = -IIk=1n [(z - a(k))((w) over bar - (a) over bar (k)) - R-2]. The main rc-sult of the paper states that in the case when the nodes a(j) are situated at the vertices of a regular n-gon inscribed in the unit circle, the matrix Q (a(i), a(j)) is positive definite if and only if R < rho(n), where z = 2 rho(2)(n) - 1 is the smallest not equal -1 zero of the Jacobi polynomial P-v(n-2v,-1) (z), v = [n/2].