Prime Number Five is very easy mathmatic memory game. Contain 30 cards. All cards has frontside number and backside number. Each card, frontside and backside has a some relation. Backside numbers are 2, 3, 5, 7, and 11. (5 types number x 6 cards) Frontside numbers are 4, 6, 9, 10, 14, 15, 21, 22, 25, 33, 35, 49, 55, 77, and 121. (15 types number x 2 cards) If frontside number is 14, then the card's backside is 2 or 7. Because 14=2x7 If backside number is 3, then the card's frontside is 6, 9, 15, 21, or 33. Shuffle all cards, and spread them on table. In your turn, reveal one card and another. If the two cards's frontside numbers are same, you get it. Get, or not get, next player's turn. —description from the publisher