A number with only two factors, 1 and itself, is a prime number.
Let's say that we have the number 3. How do we know that 3 is a prime number?
Well, it is pretty simple: just list the factors of the number.
Factors of 3:
3: 1 and 3.
From what we said earlier, a prime number only has two factors, 1 and itself. So, that means that 3 is a prime number!
Sheet 1 What are Prime Numbers