import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner input = new Scanner(System.in);
		int num = input.nextInt();
		int [] a = new int[num];
		int i, j, k;
		
		for(i = 2, k = 0; i < num; i++)
		{
			int flag = 0;
			for(j = 2; j <= i/2; j++)
			{
				if(i % j == 0)
					flag = 1;
			}
			if(flag == 0)
			{
				a[k] = i;
				k++;
			}
		}
		
		System.out.print(a[0]);
		for(i = 1; i < k; i++)
			System.out.print("," + a[i]);
		
		input.close();
	}

}

方法2：
import java.util.*; 
public class Main{
	
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
	    int N = scan.nextInt();
	    int i, j, k = 0;
	    for(i = 2; i <= N; i++) {
	    	int flag = 0;
	    	for(j = 2; j < i; j++) {
	    		if(i%j == 0) {
	    			flag = 1;
	    		}
	    	}
	    	if(flag == 0) {
	    		if(k == 0)
	    			System.out.print(i);
	    		else
	    			System.out.print("," +i);
	    		k++;
	    	}
	    }
	    
	    scan.close();
	}
}