A <em>factor</em> is a number that your number is divisible by.
19 has two factors: 19 and 1. 23 also has two factors: 23 and 1.
21 has four factors: It is divisible by 21 and 1, but also by 3 and 7. 25 has three factors: It is divisible by 25, 1, and 5.
We need a number less than 19 that has five or more factors. What we can do is multiply a bunch of numbers together (so that we know that our number will be divisible by them) to give it a lot of factors.
Let's try 2 × 2 × 3. This gives us 12.
12 has <em>six</em> factors: 12, 1, 2, 6, 3, and 4.
