The goal is to combine the blocks to get prime numbers. When a prime number is found, the blocks will explode and drop those above which can in turn train primes and so on. There are 4 modes: - original mode : no limit, for training - timed mode : you have 45s to make the biggest score you can, you'll get time bonus for each primes - survival mode : the time to make a move is decreasing, if you don't made a move when the time is elapsed, the game is over - 501 mode : like darts, you need to decrease the score to zero