Factorial

What is factorial?
Product (multiplication) of all positive integers (including 0) less than or equal to $N$. In other words, multiply all numbers from $n$ to 1.

$n$	$n!$
0	1
1	1
2	2 × 1 = 2
3	6
4	24
5	120
6	720
7	5040
8	40320
9	362880
10	3628800
…	…

Examples:

• $4!$ = 4 × 3 × 2 × 1 = 24
• $7!$ 7 × 6 × 5 × 4 × 3 × 2 × 1 = 5040
• $1!$ 1
• $10!$ 10 × 9 × 8 × 7 × 6 × 5 × 4 × 3 × 2 × 1 = 3628800

10! = 10 × 9!, … and 125! = 125 × 124!, etc. How this can be described in a formula?

$$n!=n\times (n-1)!$$

Where $n-1!$ is just part of $n!$.

External links

• Factorial Function !