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winning strategy with residue classes modulo n

Source: 2019 Austrian Federal Competition For Advanced Students, Part 1 p3

March 4, 2020
number theorygamewinning strategycombinatoricsgame strategyAustria

Problem Statement

Let n2n\ge 2 be an integer. Ariane and Bérénice play a game on the number of the residue classes modulo nn. At the beginning there is the residue class 11 on each piece of paper. It is the turn of the player whose turn it is to replace the current residue class xx with either x+1x + 1 or by 2x2x. The two players take turns, with Ariane starting. Ariane wins if the residue class 00 is reached during the game. Bérénice wins if she can prevent that permanently. Depending on nn, determine which of the two has a winning strategy.