质数概念: 只能被1和自己整除的数
public class Test3 {public static void main(String[] args) {int sum=0;for (int i = 1; i <=10000000; i++) {if (isPrime(i)) {sum++;}}System.out.println(sum);}private static boolean isPrime(int i) {for (int j =2; j <=Math.sqrt(i); j++) {if (0==i%j) {return false;}}return true;}}