Factorial numbers are calculated by multiplying all natural numbers from 1 up to and including a given number. For example, 4! = 1 x 2 x 3 x 4. In general, n! is calculated as n x (n-1) x (n-2) x ... x 2 x 1. Factorial numbers were originally denoted with an exclamation point rather than the modern notation. They are used in various mathematical exercises and calculations.

1. Damian Bogdan
Rusu Alexandru
Stroe Maria
Vanghelescu David

2. DEFINITION
If you multiply the series of all the natural numbers
that are smaller or equal to that number, you get a
factorial number. Here is an example:
4!=1 x 2 x 3 x 4
Rule: n!=n x (n-1) x (n-2) x ... x 2 x 1

3. INTERESTING FACTS
 Before the final
notation, this was
the sign:

4. Did you guess the rule?
6!=6 x 5!=1 x 2 x 3 x 4 x 5 x 6=720
Did you guess the rule?
n!=n x (n-1)!
 We usually pronounce 4!, ‘4 factorial’, but others even
say ‘4 bang’ or ‘4 shriek’.

5. Practice, practice, practice…
 What do we use factorial
numbers for? Here are
some exersises for
practice:
 7!/5!=?
 0! x 3!=?
 5!-4!-3!=?
 125!/124!=?
 n!/(n-1)=?

6. Bibliography
www.mathisfun.com
www.wolframmathworld.com