很早以前 ,人们就思索正整数的分解 ,看一个正整数是几个正整数的乘积 ,也就是一个正整数能被哪些正整数整除的问题 .除了 1和它自己而外的任何正整数都不能整除它时 ,称它为素数或质数 .例如 ,2是最小的素数 ,也是惟一的偶素数 ,在奇数当中 ,最小的素数是 3 ,此外 ,5 ,7,1 1 , Very long ago, people considered the decomposition of positive integers to see if a positive integer is the product of several positive integers, that is, the question of which positive integer can be divisible by which positive integers. All positive integers except 1 and itself are When it cannot be divisible, it is called a prime or prime number. For example, 2 is the smallest prime number, and is the only even prime number. Among the odd numbers, the smallest prime number is 3, and in addition, 5, 7, 1 1 ,