103 LearnersLast updated on July 4th, 2025
Composite Numbers
Numbers are classified into different types based on their properties. Composite numbers are the numbers with more than two factors. In this topic, we will learn about the concepts of composite numbers.
What are Composite Numbers in Math?
Numbers are of two types based on how many factors they have, prime and composite numbers. Composite numbers are the numbers that have more than two factors. Composite numbers are divisible by more than two integers. For instance, 8 is a composite number, as 1, 2, 4, and 8 are the factors of 8. The smallest composite number is 4 because 1, 2, and 3 are only divisible by 1 and the number itself. These natural numbers have more than two factors. Furthermore, if a number has only 2 factors, 1 and the same number, it is called a prime number.
History of Composite Numbers
By looking at the history of composite numbers, we can understand the development and relationship of numbers. For beneficial reasons, such as trade, measurements, and documentation, numbers were recognized by ancient civilizations like the Mesopotamians and Egyptians. Mesopotamians and Egyptians used numbers, but they were not the pioneers in defining composite numbers. In Ancient Greece, Pythagoreans classified numbers into even, odd, prime, and composite according to the nature of the numbers. Around 300 BCE, Euclid introduced the first official explanation for composite numbers. He stated that these numbers can be defined as the product of two small numbers.
During the 16th and 17th centuries, Leonhard Euler introduced significant theorems about primes, composites, and divisors. Nowadays, modern cryptography relies on composite numbers to simplify processes when working with huge numbers and prime factorization.
Properties of Composite Numbers
The numbers with more than 2 factors are composite. Composite numbers are the products of their prime factors as well. Here, are a few properties of composite numbers:
Small integers, whether they are prime or composite, can completely divide a composite number.
- Composite numbers are formed by combining two or more prime numbers.
- A composite number can be divided precisely in a variety of ways.
For example,
12 ÷ 2 = 6
12 ÷ 3 = 4
12 ÷ 4 = 3
- Composite numbers may be odd or even.
- 4 is the smallest composite number.
- 2 is the only even prime number, as all the other even numbers are composite.
- In the prime factorization process, a composite number has repeated prime factors.
Classification of Composite Numbers
A composite number can be divided precisely in a variety of ways. Composite numbers are classified by how many factors a number possesses and its characteristics. Composite numbers are greater than 1. They have more than two independent factors; also, they can be divided evenly by numbers other than 1 and themselves. In the fields of cryptography, number theory, and factorization, composite numbers are essential.
Even composite numbers
The first category of composite numbers is even composite numbers. It is possible to divide even composite numbers by 2. For example, 4, 6, 8,… 60, 78, etc. are some examples of even composite numbers. These numbers have more than two factors. For instance, the factors for the number 66 are 1, 2, 3, 6, 11, 22, 33, and 66.
Odd composite numbers
The next one is odd composite numbers. These numbers cannot be divided by 2. The numbers such as 9, 15, 21, and 25 are some of the few examples of these numbers. Additionally, these natural numbers include more than two factors.
Square composite numbers
Square composite numbers are perfect squares that are also composite, like 4, 9, 16. These are a specific type of square numbers, which are the product of multiplying a number by itself.
For example, 4, 9, 16, 25, and 36 are some examples of square composite numbers.
Non-Examples of Composite Numbers
Non-composite numbers are the numbers that are not composite and do not have more than two factors. They are the prime numbers, 1 and 0.
Prime numbers are greater than 1; these natural numbers are divisible only by 1 and the number itself. The number 1 is not a prime or composite number because it only has one divisor, that is 1 itself. Zero is not a composite number because zero has an infinite number of divisors.
Examples of Composite Numbers
Examples of composite numbers help us to understand the concept much more easily. These numbers have more than 2 factors, and they are larger than 1.
The first 10 even composite numbers are: 4, 6, 8, 10, 12, 14, 16, 18…
The first 10 odd composite numbers are: 9, 15, 21, 25, 27, 33, 35, 39, 45, 49…
The first 10 square composite numbers are: 4, 9, 16, 25, 36, 49, 64, 81, 100, 121…
Non-Examples of Composite Numbers
Understanding the non-composite numbers enables us to develop a deep understanding of the essential components of the topic.
The first few prime numbers, which are non-examples of composite numbers are: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29…
Importance of Composite Numbers for Students
Composite numbers are a vital cornerstone of mathematical comprehension. Students can concentrate on advanced math if they have a stronger grasp of composite numbers. It aids in their understanding of number theory concepts. Composite numbers are essential for doing prime factorization and solving difficult mathematical calculations. Learning the rules of division also requires an understanding of composite numbers.
Types of Numbers Related to Composite Numbers
Composite numbers are the natural numbers that are larger than 1 with more than two factors. Prime numbers, factors, multiples, the highest common factor (HCF), and least common multiple (LCM) are numbers closely related to composite numbers.
Prime Numbers
Prime numbers are natural numbers that do not have any other positive factors except 1, and the same numbers are called prime numbers. Every composite number is the product of prime numbers, and the process is known as prime factorization.
The prime factorization of 12 is 2 × 2 × 3. Here, 2 and 3 are prime numbers, even though 12 is a composite number.
2, 3, 5, 7, 11, 13, 17, 19, 23, and 29 are some examples of prime numbers.
Co Prime Numbers
Co prime numbers are pairs of numbers which have only 1 as a common factor, that is their greatest common factor (GCF) is 1. An example of co prime numbers is 8 and 15. The greatest common divisor of both numbers is 1.
Factors and Multiples
Factors are the numbers that divide another number evenly, with zero remainder. The main feature of composite numbers is that they have more than 2 factors. Take a look at this: 1, 2, 3, 4, 6, and 12 are the factors of 12.
The number we get while multiplying a number by another integer is called a multiple. It is the product of two numbers. To understand better, multiples of 3 include 3, 6, 9, 12, and so on.
Highest Common Factor (HCF)
HCF is the largest common divisor that divides two or more numbers with zero remainder. When comparing composite numbers, HCF helps to identify the biggest common factor of two or more numbers. 6 is the HCF of 12 and 18.
Least Common Multiple (LCM)
The least common multiple of two or more numbers is known as LCM. It will be a multiple of both numbers. 20 is the LCM of 4 and 5.
Tips and Tricks to Identify Composite Numbers
Identifying composite numbers from a sequence is sometimes tricky. Here are some of the tips and tricks to figure out the composite numbers:
Use divisibility rules: When we determine the factors of a larger number, we follow divisibility rules. If a number is even, then the number is divisible by 2. Also, if the last digit of a number is 0 or 5, then the number is divisible by 5.
Find the small prime numbers: If a number has more than two factors, then the number is a composite. Similarly, a number is considered prime if it contains just two factors.
Apply prime factorization: Prime factorization is a process of dividing a number into its factors. If a number has factors other than 1 and itself, we can consider it a composite number.
Remember the smallest composite number: Always remember that 4 is the smallest composite number. 1 is neither a composite nor a prime number. 2 and 3 are prime numbers. The next digit is 4, and has multiple factors.
Common Mistakes and How to Avoid Them with Composite Numbers
Students may also make several common errors while dealing with composite numbers. Here are some common mistakes and their solutions. Avoiding these errors will help students make accurate calculations.
Mistake 1
Confusion between prime and composite numbers
Sometimes students get confused about prime and composite numbers. If we assume a composite number as a prime, whether it is an odd number or a product of a prime number, the calculation becomes wrong. For example, kids mistakenly assume that 9 is a prime number, but it is a composite number.
Mistake 2
Assuming 1 as a composite number
Always remember that 1 is not a prime or composite number. The only divisor of the number 1 is the digit itself. A composite number possesses two or more factors.
Mistake 3
Incorrect prime factorization
When we divide or break a large number into small terms according to their prime factors, the process is not easy for everyone. A composite number has multiple factors. While we do prime factorization, take the smallest prime numbers. Otherwise, the calculation will lead to errors.
The prime factorization of the composite number 12 is 22 × 31.
When we start the prime factorization process, begin with the smallest prime number, 2. Then we can move on to the next prime numbers.
Mistake 4
Neglecting divisors
While we find the factors of a number, don’t stop it too early. Sometimes kids miss factors due to carelessness. So, check for every possible prime factor. For example, assuming 28 as a prime number by only testing divisibility by 2 is wrong. The number 28 has multiple factors such as 1, 2, 4, 7, 14, and 28.
Mistake 5
Considering all the even numbers are composite
Be careful that all the even numbers are not composite. For example, the smallest even number is 2. But it is not a composite number. The smallest even composite number is 4. Likewise, not all the odd numbers are composite. While you solve composite numbers, be careful about the nature of each number.
Real-World Applications of Composite Numbers
Composite numbers are essential to many sectors. It includes everything from music and entertainment to security procedures and encryption. Composite numbers and their characteristics are crucial for securing online transactions and communications. To determine the dimensions and units related to the buildings and the arrangement of products we use composite numbers. To plan and arrange events systematically, composite numbers are helpful. In music theory, the structure of beats and rhythmic constructions rely on composite numbers. Composite numbers have an infinite number of practical uses.
Solved Examples on Composite Numbers
Problem 1
Check if 105 is a composite number.
Yes. 105 is a composite number.
Explanation
First, we need to check the factors of 105. If this number has more than two factors, we can consider it as a composite number.
105 is divisible by 1, 3, 5, 7, 15, 21, 35, and 105.
For example,
105 ÷ 3 = 35
105 ÷ 5 = 21
105 has more than 2 factors. Hence, it is a composite number.
Problem 2
Check the sum of two composite numbers, 14 and 36 are composite.
14 and 36 are composite. Their sum is 50. It is also a composite number.
Explanation
When we add both composite numbers:
14 + 36 = 50
Next, we have to find out whether 50 is a composite number or not.
Since 50 has multiple factors such as 1, 2, 5, 10, 25, and 50, it is a composite number.
Problem 3
Is 101 a composite number or not?
No, 101 is not a composite number because it is only divisible by 1 and 101.
Explanation
101 is a prime number. It is greater than 1 and has only divisors as 1 and itself.
101 × 1 = 101
Problem 4
Galton has 12 chocolates. He wants to give them to his friends in equal amounts. How can he do this?
To find the answer, we need to find the factors of 12.
The factor of 12 includes 1, 2, 3, 4, 6, and 12.
So, Galton has only one friend, he gets 12 chocolates.
Likewise:
- 2 friends = 6 chocolates
- 3 friends = 4 chocolates
- 4 friends = 3 chocolates
- 6 friends = 2 chocolates
- 12 friends = 1 chocolate
Explanation
Galton can distribute 12 chocolates in different ways to his friends depending on how many friends he has.
Problem 5
Check if 150 is a composite number.
Yes. 150 is a composite number. The factors of 150 are 1, 2, 3, 5, 6, 10, 15, 25, 30, 50, 75, and 150. Since 150 has more than two factors, it is not a prime number
Explanation
150 is a composite number. Because these factors can evenly divide 150 without any remainder.
FAQs on Composite Numbers
1. What is a composite number?
2. Is 2 a composite number?
3.What is the smallest composite number?
4.How many composite numbers are between 1 and 50?
5. Is 9 the smallest odd composite number?
6. List the first 10 composite numbers.
7.Is there any number that is both prime and composite?
8.Is 11 a prime or composite number?
9.How to identify a composite number?
10.Is 1 a composite or prime number?
11.How can children in Vietnam use numbers in everyday life to understand Composite Numbers?
12.What are some fun ways kids in Vietnam can practice Composite Numbers with numbers?
13.What role do numbers and Composite Numbers play in helping children in Vietnam develop problem-solving skills?
14.How can families in Vietnam create number-rich environments to improve Composite Numbers skills?
