# Factors of 21

Last Updated: May 27, 2024

## Factors of 21

The factors of a number is a fundamental aspect of mathematics. The number 21 is a composite number, meaning it has multiple factors. Factors are numbers that divide another number exactly without leaving a remainder. For 21, these factors are 1, 3, 7, and 21. Identifying these factors is useful in various mathematical contexts, such as simplifying fractions, finding common denominators, and solving equations. The number 21’s factorization also includes both positive and negative pairs, enhancing its applications in different mathematical problems. Exploring the factors of 21 helps in grasping essential concepts in number theory and arithmetic.

## What are the Factors of 21?

The factors of 21 are 1, 3, 7, and 21. These numbers divide 21 evenly without leaving a remainder. As a composite number, 21 has several factors. Knowing these factors helps in simplifying fractions, finding common denominators, and solving mathematical problems, offering essential insights into number theory and arithmetic.

## Factors Pairs of 21

The factor pairs of 21 are:

• (1, 21): When 1 is multiplied by 21, the product is 21.
• (3, 7): When 3 is multiplied by 7, the product is 21.
• (-1, -21): When -1 is multiplied by -21, the product is 21.
• (-3, -7): When -3 is multiplied by -7, the product is 21.

These pairs include both positive and negative factors that multiply together to equal 21.

## How to Calculate Prime Factors of 21?

Calculating the prime factors of a number involves breaking it down into its basic prime number components. Prime numbers are those that have no divisors other than 1 and themselves. For composite numbers like 21, this process helps in understanding its structure and simplifying mathematical operations. Here’s how you can calculate the prime factors of 21.

• Begin with the smallest prime number, which is 2. Check if 21 is divisible by 2. Since 21 is an odd number, it is not divisible by 2.

## Step 2: Move to the Next Prime Number

• Move to the next smallest prime number, which is 3. Check if 21 is divisible by 3. Since 21 ÷ 3 = 7, and 7 is a whole number, 21 is divisible by 3.

## Step 3: Continue with the Quotient

• The quotient obtained from the previous step is 7. Check if 7 is a prime number. Since 7 has no divisors other than 1 and itself, it is a prime number.

## Step 4: List All Prime Factors

• Combine the prime factors identified. The prime factors of 21 are 3 and 7.

Therefore, the prime factorization of 21 is 3 × 7.

## Example 1: Identifying Factors of 21

• Problem: Determine the factors of 21.
• Solution: The factors of 21 are the numbers that divide 21 exactly without leaving a remainder. These numbers are 1, 3, 7, and 21.
• Answer: 1, 3, 7, 21

## Example 2: Sum of Factors of 21

• Problem: Find the sum of all factors of 21.
• Solution: The factors of 21 are 1, 3, 7, and 21. Add these factors together: 1 + 3 + 7 + 21 = 32.

## Example 3: Product of Factor Pairs of 21

• Problem: Calculate the product of the factor pair (3, 7) of 21.
• Solution: Multiply the pair of factors: 3 × 7 = 21.

## Example 4: Prime Factorization of 21

• Problem: Perform the prime factorization of 21.
• Solution: Divide 21 by the smallest prime number (3) to get 7. Since 7 is a prime number, the prime factorization of 21 is 3 × 7.

## Example 5: Checking Divisibility by Factors of 21

• Problem: Verify if 21 is divisible by 7.
• Solution: Divide 21 by 7. Since 21 ÷ 7 = 3, which is a whole number, 21 is divisible by 7.
• Answer: Yes, 21 is divisible by 7.

## Factors of 21 : Tips

The factors of a number is crucial for various mathematical applications. The number 21 is a composite number with several factors. Knowing these factors can help simplify fractions, solve equations, and understand number theory. Here are some tips to work with the factors of 21 effectively.

1. Determine all factors: The factors of 21 are 1, 3, 7, and 21. These numbers divide 21 exactly without any remainder.
2. Identify factor pairs: Factor pairs of 21 are (1, 21) and (3, 7). These pairs multiply together to result in 21.
3. Utilize prime factorization: The prime factors of 21 are 3 and 7. The prime factorization is 3 × 7.
4. Simplify fractions: Use the factors of 21 to simplify fractions where 21 is in the numerator or denominator.
5. Solve mathematical problems: Knowing the factors can aid in solving equations involving 21, such as finding roots in quadratic equations.
6. Check divisibility: Use the factors to quickly determine if 21 is divisible by another number, like 3 and 7.
7. Apply in practical scenarios: Use factors in real-world applications like dividing items into equal groups or understanding ratios.
8. Enhance understanding of number theory: Studying the factors of 21 can improve your grasp of divisibility rules, prime numbers, and composite numbers.

## What is the sum of the factors of 21?

The sum of the factors of 21 is 1 + 3 + 7 + 21 = 32.

## How is the prime factorization of 21 expressed?

The prime factorization of 21 is expressed as 3 × 7.

## What is the greatest common factor (GCF) of 21 and 28?

The greatest common factor of 21 and 28 is 7, as it is the largest number that divides both without a remainder.

## Are there any even factors of 21?

No, there are no even factors of 21 because 21 is an odd number and cannot be evenly divided by 2 or any other even number.

## What are multiples of 21?

The multiples of 21 are: 21, 42, 63, 84, 105, 126, 147, 168, 189, 210.

## What is the smallest factor of 21?

The smallest factor of 21 is 1.

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