IMO Shortlist 2016 problem N2
Dodao/la:
arhiva3. listopada 2019. Let $\tau(n)$ be the number of positive divisors of $n$. Let $\tau_1(n)$ be the number of positive divisors of $n$ which have remainders $1$ when divided by $3$. Find all positive integral values of the fraction $\frac{\tau(10n)}{\tau_1(10n)}$.
Izvor: https://www.imo-official.org/problems/IMO2016SL.pdf