Prime numbers are numbers that are only divisible by themselves and 1. For example, 3 is a prime number, but 4 isn't (because 4 is divisible by 2). You can think of prime numbers as very small families: they only ever have two people in them! Only themselves and 1. You can't fit any other numbers into them with nothing left over. 5 is one of these lonely numbers (only 5 × 1 = 5), but you can see that 6 has 2 and 3 in its family as well (6 × 1 = 6, 2 × 3 = 6). So 6 is not a prime number. Use the arrow keys to navigate around the board and to avoid the Troggles. Press the spacebar to eat a number.