Is 231 a prime number or a composite number?

A Prime number is a number with two and only two factors: 1 (also known as unity) and itself. A composite number is a number with more than two factors; in other Words, it has at least one factor besides 1 and itself. 231 has factors other than 1 and itself, so it is not a prime number. For example, it is divisible by 3. (You can check this by adding the digits of the number: 2 + 3 + 1 = 6. If the sum of the digits is divisible by 3, the number is also divisible by 3.) Therefore, 231 is a composite number.