**Two numbers are said to be 'relatively prime' if their greatest common factor is 1** 2 and 9 **are** relatively prime. Because they share no common factors: - 2: factors `[1, 2]` - 9: factors `[1, 3, 9]` No number other than "1" is shared. Therefore they are, by definition, _relatively prime_. 9 and 27 are **not** relatively prime, because their [[Greatest Common Factor]] is > 1 (it's 3). **** # More ## Source - [This page](https://www.splashlearn.com/math-vocabulary/relatively-prime) ## Related - [[Primitive Root]]