All prime numbers are odd except for the number two. A prime number is defined as any whole number greater than one that has no positive divisors except for one and itself. Since two can only be divided by the numbers one and two, it is prime. The composite numbers are integers having at least two prime factors, whereas a prime number has a single prime factor (itself), and the unit 1 has no prime factors at all. For example, 10 is composite, as it has two prime factors (2 and 5). 11 is notcomposite, since its only prime factor is itself.