MathDB
f(ab) =bf(a) + af(b), f(p) = 1, n/ gcd(n,f(n)) is square free

Source: 2003 Cuba MO 2.4

September 15, 2024
number theoryfunctional

Problem Statement

Let f:NNf : N \to N such that f(p)=1f(p) = 1 for all p prime and f(ab)=bf(a)+af(b)f(ab) =bf(a) + af(b) for all a,bNa, b \in N. Prove that if n=p1a1p2a1...pka1n = p^{a_1}_1 p^{a_1}_2... p^{a_1}_k is the canonical distribution of nn and pip_i does not divide aia_i (i=1,2,...,ki = 1, 2, ..., k) then ngcd(n,f(n))\frac{n}{gcd(n,f(n))} is square free (not divisible by a square greater than 11).