Question: are 5 and 7 coprime?
Answer: You can have the set of positive integers which are coprime to a given number: for example those coprime to 12 are 1,5,7,11,13,17,19,23,25, and so on. A number a is not "a coprime"; rather, "coprimeness" is a relation that may or may not hold between two numbers a and b.