A prime number (or a prime) is a natural number greater than 1 that
cannot be formed by multiplying two smaller natural numbers. A natural number
greater than 1 that is not prime is called a composite number. For
example, 5 is prime because the only ways of writing it as a
product, 1 × 5 or 5 × 1, involve 5 itself. However, 6 is
composite because it is the product of two numbers (2 × 3) that are
both smaller than 6.
