# What is 20 factorial ?

Steps to calculate factorial of 20

## How to calculate the factorial of 20

To find 20 factorial, or 20!, simply use the formula that multiplies the number 20 by all positive whole numbers less than it.

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

20! is exactly : 2432902008176640000

Factorial of 20 can be calculated as:
20! = 20 x 19 x 18 x 17 x ... x 3 x 2 x 1

The number of trailing zeros in 20! is 4

The number of digits in 20 factorial is 19.

## What Is Factorial?

A factorial is showed by an integer and an exclamation mark. In Mathematics, factorial is a multiplication procedure of natural numbers .

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

Symbolically, it is showed as "!".

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

## Factorial Formula

To find the factorial of any given number, exchange the value for n in the given solution :

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

The expansion of the formula provides the numbers to be replicated together with each other to receive the factorial of the number.

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

So the rule is : n! = n × (n−1)!

Example :
20! Factorial = 20 x 19 x 18 x 17 x ... x 3 x 2 x 1 = 20 × 19! = 2432902008176640000

## What are Factorials Used For?

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"

## Frequently Asked Questions on Factorial

### Can we have factorials for negative numbers ?

Negative integer factorials are undefined

### What Is 0!

Zero factorial or Factorial of 0 is simple, and its value is equal to 1. So, 0! = 1.