用筛法求素数的基本思想是：把从1开始的、某一范围内的正整数从小到大顺序排列， 1不是素数，首先把它筛掉。剩下的数中选择最小的数是素数，然后去掉它的倍数。依次类推，直到筛子为空时结束。如有：
1 2 3 4 5 6 7 8 9 10
11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30
1不是素数，去掉。剩下的数中2最小，是素数，去掉2的倍数，余下的数是：
3 5 7 9 11 13 15 17 19 21 23 25 27 29
剩下的数中3最小，是素数，去掉3的倍数，如此下去直到所有的数都被筛完，求出的素数为：
2 3 5 7 11 13 17 19 23 29(The basic idea of using sieve to find prime numbers is to set up the positive integers from 1 to a certain extent, and 1 are not prime numbers. The smallest number in the remaining number is a prime number, and then the multiple of it is removed. The analogy is in turn until the sieve ends when it is empty. If there are:

12345678910

111213141516171819 20

212223242526272829 30

1 is not a prime number, get rid of it. The smallest number in the remaining 2 is the prime number, and the number of 2 is removed, and the remaining number is:

3579111315171921 23252729)