You roll with three dice and then using the three figures to form a number between 1 and 42, you can use the four operations. For example 3 + 6-1 = 8, you then receive one point. You get an extra point for each adjacent square that is already taken. If you can´t make any free number you get a blob. The game ends when someone has three blotches (or whatever you determine yourself) and the one which has the most points wins.
This exercise practising concentration and mental arithmetic. It's also a lot of fun!