Eduardo thinks of a number between 1 and 20 that has exactly 5 factors what number is the thinking of?

Eduardo is thinking of the number ' 16 '.

The factors of  16 are  1,  2,  4,  8, and  16.

Here's a cool little factoid:

Almost every number has an even number of factors. The
only ones that have an odd number are perfect squares.
(They still have an even number of factors, but two of the factors
are the same number, so the list looks like an odd number long.)