# Number 21

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## Description of the number 21

21 is a natural number (hence integer, rational and real) of 2 digits that follows 20 and precedes 22.

21 is an even number, since it is divisible by 2.

The number 21 is a unique number, with its own characteristics that, for some reason, has caught your attention. It is logical, we use numbers every day, in multiple ways and almost without realizing it, but knowing more about the number 21 can help you benefit from that knowledge, and be of great use. If you keep reading, we will give you all the facts you need to know about the number 21, you will see how many of them you already knew, but we are sure you will also discover some new ones.

## how to write 21 in letters?

Number 21 in English is written as twenty-one
The number 21 is pronounced digit by digit as (2) two (1) one.

## What are the divisors of 21?

The number 21 has 4 divisors, they are as follows:

The sum of its divisors, excluding the number itself is 11, so it is a defective number and its abundance is -10

## Is 21 a prime number?

No, 21 is not a prime number since it has more divisors than 1 and the number itself

## What are the prime factors of 21?

The factorization into prime factors of 21 is:

31*71

## What is the square root of 21?

The square root of 21 is. 4.5825756949558

## What is the square of 21?

The square of 21, the result of multiplying 21*21 is. 441

## How to convert 21 to binary numbers?

The decimal number 21 into binary numbers is.10101

## How to convert 21 to octal?

The decimal number 21 in octal numbers is25

## How to convert 21 to hexadecimal?

The decimal number 21 in hexadecimal numbers is15

## What is the natural or neperian logarithm of 21?

The neperian or natural logarithm of 21 is.3.0445224377234

## What is the base 10 logarithm of 21?

The base 10 logarithm of 21 is1.3222192947339

## What are the trigonometric properties of 21?

### What is the sine of 21?

The sine of 21 radians is.0.83665563853606

### What is the cosine of 21?

The cosine of 21 radians is. -0.54772926022427

### What is the tangent of 21?

The tangent of 21 radians is.-1.5274985276366