Common factor, also known as "common divisor". Is an integer that can be divided by several integers at the same time [1]. If an integer is a factor of several integers at the same time, it is called their "common factor"; The greatest common factor is called the greatest common factor.

Given several integers, if a number is the same factor as them, then this number is called their common factor. The greatest common factor of all these integers is called the greatest common factor of these integers.

The common divisor is opposite to the common multiple, that is, it is both the divisor of A and the divisor of B. The common divisor of 12 and 15 is 1 3, and the greatest common divisor is 3. For another example, 30 and 40, their common divisor is 1, 2,5, 10, and the greatest common divisor is 10.