Start with the numbers 1, 2, 3, 4, 5, 6, 7, 8, and 9. You and an opponent taking turns picking numbers, each time a number that has not been picked before. The

Start with the numbers 1, 2, 3, 4, 5, 6, 7, 8, and 9. You and an opponent taking turns picking numbers, each time a number that has not been picked before. The winner is the first person to have picked three numbers that sum to exactly 15. Try it out with a friend. You will gradually realize that it it seems surprisingly familiar...