Prime numbers are whole numbers greater than 1 that have exactly two factors: 1 and the number itself. Composite numbers are whole numbers greater than 1 that have more than two factors.
The number 1 is neither prime nor composite because it has only one factor: 1.
To decide if a number is prime or composite, check how many factors it has. A factor is a number that divides evenly into another number without leaving a remainder.
Even numbers greater than 2 are always composite because they are divisible by 2.
Here is a list of prime numbers between 1 and 50. These are good to memorize because they appear often in math problems.
2 is the only even prime number. Every other even number is divisible by 2 and therefore composite.
Finding all factors of a number helps confirm if it is prime or composite. If a number has only two factors, it is prime. If it has three or more, it is composite.
You can use multiplication facts to find factors quickly. For example, 3 × 4 = 12, so 3 and 4 are factors of 12.
Prime and composite numbers are important for understanding multiplication, division, and fractions. Prime numbers are the “building blocks” of all other numbers because every composite number can be written as a product of primes.
This process is called prime factorization. It shows how a composite number can be broken into a product of prime numbers.