Factors of 21
Factors of 21 are integers that can be divided evenly into 21. It has a total of 4 factors of which 21 is the biggest factor and the positive factors of 21 are 1, 3, 7, and 21. The sum of all factors of 21 is 32 and its factors in Pairs are (1, 21) and (3, 7).
 Factors of 21: 1, 3, 7 and 21
 Negative Factors of 21: 1, 3, 7 and 21
 Prime Factors of 21: 3, 7
 Prime Factorization of 21: 3 × 7 = 3 × 7
 Sum of Factors of 21: 32
1.  What Are the Factors of 21? 
2.  How to Calculate Factors of 21? 
3.  Factors of 21 by Prime Factorization 
4.  Factors of 21 in Pairs 
5.  FAQs on Factors of 21 
What are the Factors of 21?
To have an answer to this question let us have a look at the following facts about factors of 21:
 The factor of 21 is that number that divides 21 completely i.e., without any remainder.
 The number 21 is composite. To understand why it is composite, let's recall the definition of a composite number. "A number is said to be composite if it has more than two factors
 The factors of 21 are all the integers that divide 21 without any remainder.
 According to the definition, the justified factors of 21 are 1, 3, 7, and 21.
How to Calculate the Factors of 21?
Let's begin calculating the factors of 21, starting with the smallest whole number i.e. 1
 Divide 21 with this number. Is the remainder 0?
 21 ÷ 1 = 21
 The next whole number is 3
 21 ÷ 3 = 7
 The next whole number is 7
 21 ÷ 7 = 3
Hence, the factors of 21 are 1, 3, 7, and 21.
Explore factors using illustrations and interactive examples.
 Factors of 121  The factors of 121 are 1, 11, 121
 Factors of 210  The factors of 210 are 1, 2, 3, 5, 6, 7, 10, 14, 15, 21, 30, 35, 42, 70, 105, 210
 Factors of 216  The factors of 216 are 1, 2, 3, 4, 6, 8, 9, 12, 18, 24, 27, 36, 54, 72, 108, 216
 Factors of 27  The factors of 27 are 1, 3, 9, 27
 Factors of 42  The factors of 42 are 1, 2, 3, 6, 7, 14, 21, 42
 Factors of 35  The factors of 35 are 1, 5, 7, 35
Factors of 21 by Prime Factorization
"Prime factorization means to express a composite number as the product of its prime factors." To get the prime factorization of 21, we will follow the below process:
 Divide 21 by its prime factor, say 3
 21 ÷ 3 = 7
 7 is divided by its prime factor and the quotient is obtained.
 This process goes on till we get the quotient as 1
 7 ÷ 7 = 1
 We find that 21 has a total of 2 prime factors.
The prime factorization of 21 is shown below:
Factors of 21 in Pairs
The pair of numbers which gives 32 when multiplied is known as factor pairs of 21. The following are the factors of 21 in pairs.
Product form of 21 
Pair factor 
1 × 21 = 21 
(1, 21) 
3 × 7 = 21 
(3, 7) 
7 × 3 = 21 
(7, 3) 
21 × 1 = 21 
(21, 1) 
 Observe in the table above, after 3 × 7, the factors start repeating accept the order.
 So, it is enough to find factors until (3, 7)
 Pairs of factors of 21 are: (1, 21), (3, 7)
Fractions or decimals cannot be the factors. Only integers (positive or negative) can be the factors.
 Factors of 21 are 1, 2, 7, and 21.
Factors of 21 Solved Examples

Example 1: Can you help Mark list the factors of 12 and factors of 21?
Solution:
Factors of 12 and 21 are the numbers that divide exactly without any remainder.
Factors of 12 are as follows:
12 ÷ 1 = 12
12 ÷ 2 = 6
12 ÷ 3 = 4
12 ÷ 4 = 3
12 ÷ 6 = 2
12 ÷ 12 = 1
Factors of 21 are as follows:
21 ÷ 1 = 21
21 ÷ 3 = 7
21 ÷ 7 = 3
21 ÷ 21 = 1
Hence, factors of 12 are 1, 2, 3, 4, 6 and 12
Factors of 21 are 1, 3, 7, and 21 
Example 2: Three friends bought 21 candies from a shop and distributed them among themselves equally. How many would each one of them get?
Solution:
21 candies are to be divided among 3 friends equally.
This implies we need to divide 21 by 321 ÷ 3 = 7
Hence, each friend will get 7 candies.

Example 3: Find the Least Common Multiple (LCM) and Greatest Common Factor (GCF) of 21 and 11.
Solution:
The factors of 21 are 1, 3, 7, 21, and factors of 11 are 1, 11.
Therefore, the Least Common Multiple (LCM) of 21 and 11 is 231 and the Greatest Common Factor (GCF) of 21 and 11 is 1.
FAQs on Factors of 21
What are the Factors of 21?
The factors of 21 are 1, 3, 7, 21 and its negative factors are 1, 3, 7, 21.
What is the Sum of the Factors of 21?
All the Factors of 21 are 1, 3, 7, 21 and therefore the sum of all these factors is 1 + 3 + 7 + 21 = 32
What is the Greatest Common Factor of 21 and 15?
The factors of 21 and 15 are 1, 3, 7, 21 and 1, 3, 5, 15 respectively.
Common factors of 21 and 15 are [1, 3].
Hence, the GCF of 21 and 15 is 3.
How Many Factors of 21 are also common to the Factors of 18?
Since, the factors of 21 are 1, 3, 7, 21 and the factors of 18 are 1, 2, 3, 6, 9, 18.
Hence, [1, 3] are the common factors of 21 and 18.
What are the Prime Factors of 21?
The prime factors of 21 are 3, 7.