Every compound number can be written as a number multiply formality. The number both are the combined number divisor, which is called the combined number divisor. The decomposer divisor is only for a number.

As a simple example, 12's decomposition divisor can have the following types: 12=2x2x3=4x3=1x12=2x6, where 1,2,3,4,6,12 can be said to be 12's divisor, that is, multiply several number be tantamount to one Nature number, then these numbers are the Nature number divisor. In 2,3,4, 2 and 3 are prime numbers, which are prime divisor, and 4 is not prime numbers. then what is prime number? That is, it can no longer be divided into an outside divisor number other than 1 and itself, such as 2,3,5,7,11,13,17,19,23,29, and so on, there is no particular law of mass number, there is no maximum mass number.