Counting to 20

Here is a counting game to try with a partner.

• The object of the game is to be the first one to say "20".
• The first person must start at "1".
• Each person may say one, two, or three numbers per turn, and the numbers must be in counting order. Each person must start with the number after the last one that the other person said.
• For example, the first person can say "1", or "1, 2", or "1, 2, 3."
• If the first person says "1, 2", then the second person could say "3" or "3, 4", or "3, 4, 5".
• Whoever says "20" wins the game.
• Play this game many times and try to discover a winning strategy.