Question

What numbers are relatively prime numbers

Answer 1

Two integers are relatively prime (or coprime) if there is no integer greater than one that divides them both (that is, their greatest common divisor is one). For example, 12 and 13 are relatively prime, but 12 and 14 are not.
A list of integers is (mutually) relatively prime if there is no integer that divides them all. For example, the integers 30, 42, 70, and 105 are mutually relatively prime (but not pairwise relatively prime).
This definition is generalized into many other areas. For example, two polynomials with integer coefficients are relatively prime if there is no non-constant polynomial which divides them both.