Orbits of rational n-sets of projective spaces under the action of the linear group

Let k = F q be a finite field. We enumerate k-rational n-sets of (unordered) points in a projective space P N over k, and we compute the generating function for the numbers of PGL N + 1 ( k ) -orbits of these n-sets. For N = 1 , 2 we obtain a formula for these numbers of orbits as a polynomial in q with integer coefficients.