On grid paper, draw a number grid from 21 to 50.

The first player selects a number from the grid and crosses it out. The player then finds the prime factorization of that number. The player is awarded the sum of the prime factors of that number, with one exception. If a factor is used more than once in the factorization, it is only used once in calculating the sum for scoring purposes. For example, if the player selects 24, he or she receives 2 + 3 or 5 points since the prime factorization of 24 is 2³ · 3.

The second player selects a number that has not been crossed out and scores the sum of the prime factors of that number. The players continue to take turns choosing numbers until all numbers have been crossed out. The player with the most points wins.