Question

what is prime or co prime numbers ?

Answer 1

Hey mate here is your answer...
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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 

Answer 2

In number theory, two integers a and b are said to be relatively prime, mutually prime, or coprime (also written co-prime) if the only positive integer (factor) that divides both of them is 1. ... This is equivalent to their greatest common divisor (gcd) being 1.