Factors of 21

Factor pairs of the number 21 are the whole numbers which could be either positive or negative but not a fraction or decimal number. The factors of a number 21 are the numbers, that produce the result as 21 when two numbers are multiplied together. To find the factors of a number, 21, we will use the factorization method.

Factors of 21

To understand this method in a better way, read the article below to find factor 21 in pairs and also the division method to find the prime factors of 21 is discussed. Some of the properties of the factor are:

  • The number 1 is a factor of every given number
  • Every number is should be a factor of a given number
  • The factor number should be less than or equal to the given number
  • For a number, there is an infinite number of factors sometimes.

Factors of 21

Factors of 21
1, 3, 7 and 21

Pair Factors of 21

To find the positive and negative factor pairs of 21, multiply the two numbers in a pair to get the original number as 21, such numbers are as follows.

Positive Pair Factors Negative Pair Factors
1 × 21 = 21 ⇒ (1, 21) -1 × -21 = 21 ⇒ (-1, -21)
3 × 7 = 21 ⇒ (3, 7) -3 × -7 = 21 ⇒ (-3, -7)

Prime Factors of 21 By Division Method

The number 21 is a composite and it should have prime factors. Now let us know how to calculate the prime factors of 21.

Step 1: The first step is to divide the number 21 with the smallest prime factor, say 3.

           21 ÷ 3 = 7

Step 2: If you divide 7 by 3, you will get a fractional value that cannot be a factor. So continue with the next prime number, say 7

7 ÷ 7 = 1

Finally, we received the number 1 at the end of the division process. So that we cannot proceed further. So, the prime factors of 21 are written as  3 x 7, where 3 and 7 are the  prime numbers.

How to calculate the Factors of 21?

Learn the following steps to calculate the factors of 21.

    • First, write the number 21
    • Find the two numbers, which gives the result as 21 under the multiplication, say 3 and 7, such as 3 × 7 = 21.
    • We know that 3 is a prime number which has only two factors, i.e., 1 and the number itself( 1 and 3). So, it cannot be further factorized.

3 = 3 × 1

    • Also, look at the number 7, which is also a prime number and it cannot be further factorised.

7 = 7 x 1

  • Therefore, the factorization of 21 is written as 21 = 3 x 7 x 1
  • Finally, write down all the unique numbers which we can be obtained as the factors of a number 21
Factors of 21
1, 3, 7 and 21

Prime Factors of 21 By Division Method

The number 21 is a composite and it should have prime factors. Now let us know how to calculate the prime factors of 21.

Step 1: The first step is to divide the number 21 with the smallest prime factor, say 3.

21 ÷ 3 = 7

Step 2: If you divide 7 by 3, you will get a fractional value that cannot be a factor. So continue with the next prime number, say 7

7 ÷ 7 = 1

Finally, we received the number 1 at the end of the division process. So that we cannot proceed further. So, the prime factors of 21 are written as 3 x 7, where 3 and 7 are the prime numbers.

Stay tuned with BYJU’S to know about factor 21 and the factors and prime factors of other numbers. Download BYJU’S – The Learning App for better experience and clarification.

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