We know that if N = p₁^a₁p₂^a₂...p_n^a_n , then number of distinct positive integers D = (a₁ + 1) * (a₂ + 1) * ... * (a_n + 1). For D = 3, we have only one possibility, that is a₁ = 2 and rest all a_i = 0. Hence, N is of the form p².