Question

What are co-prime numbers

Answer 1

Numbers, which do not have any common factor between them other than one, are called co-prime numbers.
Explanation:
When two numbers (they may not be prime) do not have any common factor other than one between them they are called co-prime or relatively prime.
It is obvious that two prime numbers are always co-prime. For example, 17 and 23.
However, even two composite numbers can also be co-prime or relatively prime. For example 16and 25 do not have any common factor other than one. Similarly 84 and 65 do not have any common factor and are hence co-prime.