Operations on 100 positive integers
Source: BMO Shortlist 2022, C1
May 13, 2023
combinatoricsnumber theory
Problem Statement
There are 100 positive integers written on a board. At each step, Alex composes 50 fractions using each number written on the board exactly once, brings these fractions to their irreducible form, and then replaces the 100 numbers on the board with the new numerators and denominators to create 100 new numbers. Find the smallest positive integer such that regardless of the values of the initial 100 numbers, after steps Alex can arrange to have on the board only pairwise coprime numbers.