Python:

def ktnt(n):
    if (n<2): return False
    for i in range (2,int(n**0.5)+1):
        if (n%i==0):
            return False
    return True
n=int(input('nhap n: '))
if (ktnt(n)==True):
    print('n la so nguyen to')
else:
    print('n khong la so nguyen to')

C++:

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

$\color{green}{\text{**Nếu cần code Java hay C# thì nói để mình bổ sung}}$

$\color{red}{\text{#Daoanhviet96}}$

uses crt;

var i,n,d: integer;

begin

clrscr;

write ('nhap n: ');  readln (n);

for i:=1 to n do  

if n mod i=0 then d:=d+1;

if d=2 then write ('day la so nguyen to')

else write ('day khong phai la so nguyen to');

readln;

end.