Problem

Source: CentroAmerican 2004

Tags: combinatorics proposed, combinatorics



On a whiteboard, the numbers $1$ to $9$ are written. Players $A$ and $B$ take turns, and $A$ is first. Each player in turn chooses one of the numbers on the whiteboard and removes it, along with all multiples (if any). The player who removes the last number loses. Determine whether any of the players has a winning strategy, and explain why.