Here are the factors of 12:

1, 2, 3, 4, 6, 12

As you can see, there are 6 factors of 12.

Write a list of all the factors of the integers 1, 2, 3, ... up to about 20.

Don't forget 1 and the number itself!

Now count them. What do you find?

Hint: Which numbers have an odd number of factors?

Why?