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MathNet 2020 — Math Olympiad Vault — Part 04 Question 110

Math Olympiad Vault · MathNet 2020 — Math Olympiad Vault — Part 04

Question 110

Alice and Bob play the following game: starting with the number $2$ written on a blackboard, each player in turn changes the current number $n$ to a number $n + p$, where $p$ is a prime divisor of $n$. Alice goes first and the players alternate in turn. The game is lost by the one who is forced to write a number greater than $\underbrace{2 \ldots 2}_{2020}$. Assuming perfect play, who will win the game.