A prime number is a natural number (the positive integers (whole numbers) 1, 2, 3, etc., and sometimes zero as well) 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.
