注意两点：Java运算时间以及1不包含在质数因子内

import java.io.*;
import java.lang.Math;
public class Main
{
    public static void main(String[] args) throws IOException
    {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String str;
        while( (str = br.readLine()) != null )
        {
            int num = Integer.parseInt(str);
            StringBuilder sb = new StringBuilder( );
            if(num==2)
            {
                sb.append("2 ");
            }
            else
            {
                for(int i = 2; i <= Math.sqrt(num); i++  )
                {
                    while(num%i==0)
                    {
                        sb.append(i).append(" ");
                        num /= i;
                    }
                }
                if( num != 1)
                {
                    sb.append(num).append(" ");
                }
            }
            System.out.println(sb);
        }
    }
}