A function over factors

A function f is defined over natural numbers as: f(N) = ∑ di μ(di) Here the summation is over di, all positive integers which are factors of N. μ(n) is the Möbius function defined in the following way: If there exists a prime p such that p2 is a factor of n, then μ(n)=0. Otherwise, if n has an odd number of prime factors, μ(n)=-1. If not, μ(n)=1. Thus the first few va