Combinatorics · Combinatorial games · Winning and losing positions · Mirroring strategy · Disjoint sums of games · Primes

Problem 3, 2014

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NationalOpen answer

A pile of \(n\) tokens lies on a table. Two players, \(A\) and \(B\), move alternately, and \(A\) moves first. In one move a player must do one of the following:

  • remove one token from one of the piles on the table, or
  • replace one of the piles by several piles - at least two of them - all containing the same number of tokens.

A pile whose last token is removed ceases to exist. The player who takes the last token from the table wins.

For which values of \(n\) does player \(A\) have a winning strategy, and for which values of \(n\) does player \(B\) have a winning strategy?

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Serbian National Competition (Drzavno takmicenje) 2014, high school grade I, category A, problem 3. Organized by the Mathematical Society of Serbia (DMS). Source