Xunzhi

[Relativistic Prime] When two numbers have only one common divisor 1, their relationship is called coprime. Such as 3 and 1 1 coprime.

5 and 5 are not coprime because the common factors of 5 and 5 are 1 and 5.

1 is a multiple of any number, but it is coprime with any number. Because the factor of 1 is only 1, and the principle of prime numbers is: as long as the common factor of two numbers is only 1, two numbers are said to be prime numbers. 1 has only one factor (so 1 is neither a prime number (prime number) nor a composite number), and it is impossible to find other common factors of 1 and other numbers, so 1 and any number are coprime.