依序判断即可 
#include<iostream>

using namespace std;
int main()
{
    int num;
    while(cin>>num)
    {
        if(num%2==0)
            cout<<"2"<<" ";
        if(num%3==0)
            cout<<"3"<<" ";
        if(num%7==0)
            cout<<"7"<<" "; 
        if(num%7&&num%2&&num%3)
            cout<<"n";
    }
    return 0;
}