Some numbers are more special than others. One particular breed of special numbers are the prime numbers (primes). These obey the simple rule:
Prime numbers can only be divided by 1 and themselves.
In other words, they ony have 2 factors. The first 4 primes are:
2, 3, 5, 7
Some people often think that 1 is a prime, but it has only one factor: so disobeys the rule.