What is 21 factorial ?

To find 21 factorial, or 21!, simply use the formula that multiplies the number 21 by all positive whole numbers less than it.

Let's look at how to calculate the Factorial of Twenty-one :

  21! is exactly : 51090942171709440000

  Factorial of 21 can be calculated as:
21! = 21 x 20 x 19 x 18 x ... x 3 x 2 x 1

  The number of trailing zeros in 21! is 4

  The number of digits in 21 factorial is 20.

• 17 Factorial
• 18 Factorial
• 19 Factorial
• 20 Factorial
• Factorial of 22
• Factorial of 23
• Factorial of 24
• Factorial of 25

A factorial is symbolized by an integer and an exclamation symbol. In Mathematics, factorial is a multiplication process of natural numbers .

It multiplies the number by every standard number that is less than it .

Symbolically, it is represented as "!".

The function is used, among other things, to get the "n" way pieces can be arranged .

To find the factorial of any given number, change the value for n in the given rule :

n! = n × (n-1) × (n-2) × (n-3) × ….× 3 × 2 × 1

The expansion of the formula shows the numbers to be replicated to each other to have the factorial of the number.

We can also work out a factorial from the prior one. The factorial of any number is that number times the factorial of (that number minus 1).

So the rule is : n! = n × (n−1)!

Example :
21! Factorial = 21 x 20 x 19 x 18 x ... x 3 x 2 x 1 = 21 × 20! = 51090942171709440000

The best use of factorial is in Combinations and Permutations.

Example : Determine how to arrange letters without repeating?

There one way for 1 letter "a":
2 ways for two letters "ab": ab, ba.
There are 6 ways for 3 letters "abc": abc acb cab bac bca.
There are 24 ways for 1234 of the letters "abcd"

21 in French

21 in English

Factors of 21