Counting Coprime Pairs Using Möbius Inversion
Möbius Function The Möbius function μ(n) is defined on positive integers with the following rules: μ(1) = 1 For n > 1: If n contains a squared prime facter (∃p: p² | n), then μ(n) = 0 Otherwise, if n has k distinct prime factors, then μ(n) = (-1)^k This function satisfies a crucial identity: $$\s...