Prime numbers are a subset, or smaller part, of the natural numbers. A prime is a natural number with exactly two distinct natural number divisors: one and itself. Or, to put it another way, a prime is a natural number that can be evenly divided only by one and itself. That is to say that if you divide a prime by any other natural number you will get other natural number you will get a fraction or decimal. There are a couple of restrictions on primes: a negative number cannot be a prime; and one itself if not a prime.

Now, composite numbers represent the ‘opposite’ of primes. A composite number is a natural number that has a positive divisor other than one and itself. This means that composite numbers represent all the natural numbers that are not prime numbers, except one. The number one is neither a prime number nor a composite number. There is always an odd one out.