using System;

public class Program

{

    public static void Main()

    {

        bool isPrime = true ;

        Console.WriteLine("Prime Numbers :");

        for (int i = 2 ; i <=20; i++)

        {

            for(int j = 2 ; j <=20; j++)

            {

                if(i !=j &&  i %j ==0)

                {

                    isPrime = false;

                    break;

                }

            }

            if(isPrime)

            {

                Console.Write("\t" +i);

            }

            isPrime = true;

            }           

        }

    }

​

​

​

// prime  number divide by 1 and iteslf 

// we have a number n 

// so n%1 == 0 and n%n == 0

//0 and 1 is also not prime