olymmath

OFM 2021 S2

  • Senior

Albert and Beatrice play a game. 20212021 stones lie on a table. Starting with Albert, they alternatively remove stones from the table, while obeying the following rule. At the nn -th turn, the active player (Albert if nn is odd, Beatrice if nn is even) can remove from 11 to nn stones. Thus, Albert first removes 11 stone; then, Beatrice can remove 11 or 22 stones, as she wishes; then, Albert can remove from 11 to 33 stones, and so on. The player who removes the last stone on the table loses, and the other one wins. Which player has a strategy to win regardless of the other player's moves?

Dataset text AI-MO AoPS. Quoted with source.

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