函数基本应用。编辑、注释、运行、调试自己编写的程序.

写一个函数,判断一个自然数是否为素数，编写判断函数和测试主函数。

-The basic function of the application. Edit, annotate, run, debug, write your own programs. Write a function to determine whether a natural number is a prime number, the preparation and testing to determine the function main function.