Câu 3:
#include <bits/stdc++.h>
using namespace std;
long long n;
int main()
{
cin>>n;
bool kt=true;
for (long long i=2; i<=sqrt(n); i++)
if (n%i==0)
{
kt=false;
break;
}
if ((kt==true) and (n>1)) cout<<"la so nguyen to";
else cout<<"khong la so nguyen to";
return 0;
}