Are there any 2 numbers that don't have a common factor?

Answer 1

Since 1, known as the "multiplicative identity", cannot be counted as a factor, there are many pairs of numbers that do not have common factors, such as 2 and 3, 2 and 5, and 3 and 5. There are many pairs of composite (not prime) numbers without common factors, such as 4 and 9.

Also, since prime numbers do not have factors, any pair of primes cannot have a common factor, though a pair in which one number is prime may, e.g. 5 and 10.