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# What is 21 factorial ?

Steps to calculate factorial of 21

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 21:

21! is exactly :
51090942171709440000
Factorial of 21 can be calculated as:
21! = 21 x 20 x 19 x 18 x 17 x 16 x 15 x 14 x 13 x 12 x 11 x 10 x 9 x 8 x 7 x 6 x 5 x 4 x 3 x 2 x 1

## What is Factorial?

The concept of factorial is fundamental in mathematics, symbolized as n!. A factorial represents the product of all positive integers up to a given number n. Specifically, the factorial of 21 is vital as it is the building block for various equations and scenarios in combinatorics, probability, and other mathematical realms. Understanding the factorial of 21 can aid in solving complex problems where large permutations and combinations are involved.

## Formula to Calculate the Factorial of 21

The factorial is calculated using the formula: n! = n × (n-1) × … × 1. Applying this to 21, we calculate 21 factorial (21!) by multiplying all whole numbers from 21 down to 1. For clarification and easier understanding, let’s look at how this breaks down step by step:

21! = 21 × 20 × 19 × … × 3 × 2 × 1

## What is the Factorial of 21 Used For?

The factorial function, and specifically 21 factorial, has a plethora of fascinating applications. In combinatorics, it is used to calculate the number of ways to arrange or select items. For probability theory, it helps to ascertain the likelihood of various outcomes. The factorial of 21 may be utilized in calculating permutations in large datasets, complex scheduling problems, or certain encryption algorithms in computer science.

## Exercises

• Calculate 21! ÷ 20! and explain the result.
• Using 21!, determine how many ways 21 books can be arranged on a shelf.

## Solutions to Exercises

1. 21! ÷ 20! simplifies to 21, as 20! cancels out. This illustrates that when you divide the factorial of a number by the factorial of the preceding number, you get the original number.
2. Number of ways to arrange 21 books: Given that each book is unique, the number of ways to arrange them is equal to 21!, which is a very large number and signifies the immense possibilities of arrangements.