Problem

Source: Finland 2017, p4

Tags: game, combinatorics, game strategy, winning strategy



Let $m$ be a positive integer. Two players, Axel and Elina play the game HAUKKU ($m$) proceeds as follows: Axel starts and the players choose integers alternately. Initially, the set of integers is the set of positive divisors of a positive integer $m$ .The player in turn chooses one of the remaining numbers, and removes that number and all of its multiples from the list of selectable numbers. A player who has to choose number $1$, loses. Show that the beginner player, Axel, has a winning strategy in the HAUKKU ($m$) game for all $m \in Z_{+}$. PS. As member Loppukilpailija noted, it should be written $m>1$, as the statement does not hold for $m = 1$.