Advertisement

Grab a calculator!  I'm going to teach you about a new button.

Look for it...  It will either be

x!orn!

(It's probably above one of the other buttons.)

Find it?

It's called a factorial.

Here's an example:

5!

(No, this isn't just an excited 5.)

Here's what it means:

5! = 5 * 4 * 3 * 2 * 1 = 120
 

Check it by multiplying it out the long way, then try the button.

Here are some others:

                                             3! = 3 * 2 * 1

                                             6! = 6 * 5 * 4 * 3 * 2 * 1

                                             4! = 4 * 3 * 2 * 1

                                              2! = 2 * 1

                                                 1! = 1