And then what about seat number three? Well, if you know who's in seat number one and seat number two, there's only one person who can be in seat number three. And another way to think about it, if two people have already sat down, there's only one person who could be in seat number three. And so mathematically, what we could do is just say three times two times one. And you might recognize the mathematical operation factorial which literally just means, hey, start with that number and then keep multiplying it by the numbers one less than that and then one less than that all the way until you get to one. And this is three factorial which is going to be equal to six which is exactly what we've got here. And to appreciate the power of this, let's extend our example.