The unitary divisor function σ_k^*(n) is the analog of the divisor function σ_k(n) for unitary divisors and denotes the sum-of-kth-powers-of-the-unitary divisors function. As in the case of the usual divisor function, σ_1^*(n) is commonly written σ^*(n). The numbers of unitary divisors σ_0^*(n) is the same as the numbers of squarefree divisors of n, as well as 2^q, where q is the number of different primes dividing n. If n is squarefree, then σ(n) = σ^*(n).

divisor function | unitary amicable pair | unitary divisor