A **composite number** is a positive integer greater than 1 which is not a prime number. Composite numbers can always be written as a product of prime numbers, which represent a prime factorization.^{[1]} For example, the prime factorization of the composite number 42 is 2 x 3 x 7.

A composite number is one of two types of number that is the opposite of a prime number. Specifically, a composite number is the *general* opposite to a prime. The special opposite number to a prime is a *highly composite number* (HCN). The set of HCNs is a subset of composite number, specifically by being made of the type of composite number that has more factors than any number both lesser than itself and lesser than its higher HCN neighbor.