ANSWER
The number that fills in the blanks is 1
Step-by-step explanation
Two numbers are relatively prime if they have no common factor greater than 1.
For exam 12 and 17 have no common factor greater than 1.
This is equivalent to saying that the greatest common divisor (GCD) of the two numbers is 1.

This means that
and
are relatively prime.
But
. This means 12 and 16 are not relatively prime or coprime