The
integers
a and
b are said to be
coprime or
relatively prime
iff they have no common factor other than 1 and -1.
(In particular, 1 is coprime to every integer;
0 is coprime only to 1 and -1.) For example, 6 and 35 are coprime, but 6 and 28 are not.
In other words, a and b are coprime
iff their greatest common divisor is 1.
This is equivalent to the existence of integers
p and q such that ap + bq = 1.