Factors of 21 are those numbers that, when multiplied together, give the result of 21. We can also say that a factor is a number that divides a number ultimately, leaving zero as a remainder. We will use the multiplication method to find the factors of 21.

**Factors Calculator**

Factors of 21: 1, 3, 7 and 21

Factors of -21: -1, -3, -7 and -21

Prime Factors of 21: 3, 7

Prime Factorization of 21: 3 × 7

Factors of 21 in Pairs: (1, 21) and (3, 7)

## What are the factors of 21?

The method of calculating the factors of 21 is as follows. First, each number can be divided by one and by itself.

Consequently, 1 and 21 are the factors of 21.

By dividing a number by 1, 2, 3, 4… we can discover all its factors.

(i) 21 ÷ 1 = 21

This division gives the remainder 0 and so is divisible by 21. So please put them 1 and 21 in your factor list.

1, …….. 21

(ii) 21 ÷ 2 = 10.5

This division gives the remainder 10.5, not being thoroughly divided. So we will not write 2 and 10.5 on the list.

(iii) 21 ÷ 3 = 7

This division gives the remainder 0 and so is divisible by 7. So please put them 3 and 7 in your factor list.

1, 3 …….. 7, 21

(iv) Since we don’t have any more numbers to calculate, we are putting the numbers so far.

So 1, 3, 7 and 21 are factors of 21.

## Factors of -21

To get the factors of -21 by the multiplication method, we will first write the number -21 multiplicatively in all possible ways. We can write -21 as follows and we have:

21 = -1 × -21 Therefore, -1, -21 are factors of -21

21 = -3 × -7 Therefore, -3, -7 are factors of -21

As there are no other ways we can express -21 multiplicative, we will stop now, and we have obtained all the factors of -21.

So, the factors of -21 are -1, -3, -7 and -21

## All factors of 21

Here is a list of all the positive and negative factors of 21 in numerical order.

1, 3, 7, 21, -1, -3, -7 and -21

Therefore, 1, 3, 7, 21, -1, -3, -7 and -21 are All factors of 21.

## Factor pairs of 21

21 x 1 = 21

3 x 7 = 21

So, (1, 21) and (3, 70) are factor pairs of 21

## Prime Factorization of 21

21 ÷ 3 = 7

7 ÷ 7 = 1

Therefore, 3 × 7 are the Prime factorization of 21.

## Factor tree of 21

```
21
/ \
3 7
```

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