Abstract. Let p 1 < p 2 < · · · < p ν < · · · be the sequence of prime numbers and let m be a positive integer. We give a strong asymptotic formula for the distribution of the set of integers having prime factorizations of the form p m k 1 p m k 2 · · · p m kn with k 1 ≤ k 2 ≤ · · · ≤ k n . Such integers originate in various combinatorial counting problems; when m = 2, they arise as Matula numbers of certain rooted trees.