MathDB
Removing divisors - who wins?

Source: Daniel Harrer, problem 3 of the 4th QEDMO

November 10, 2007
combinatorics proposedcombinatorics

Problem Statement

Let n n be a positive integer, and let M\equal{}\left\{ 1,2,...,n\right\}. Two players take turns at the following game: Each player, at his turn, has to select an element of M M and remove all divisors of this element (including this element itself) from the set M M. a) Assume that the player who cannot move anymore (because the set M M is empty when it's his move) wins. For which values of n n does the first player have a winning strategy? b) Assume that the player who cannot move anymore (because the set M M is empty when it's his move) loses. For which values of n n does the first player have a winning strategy?