How to check a number if it's prime number or not?

after we learn about alghorithm on a prime number, i will show you the code to make prime number !

using System;
namespace example
{
    class prime
    {
        public static void Main()
        {
            Console.Write("Enter a Number : ");
            int n;
            n = Convert.ToInt32(Console.ReadLine());
            int k;
            k = 0;
            for (int i = 1; i <= n; i++)
            {
                if (n % i == 0)
                {
                    k++;
                }
            }
            if (k == 2)
            {
                Console.WriteLine("This is Prime Number");
            }
            else
            {
                Console.WriteLine(" This is Not Prime Number");
            }
            Console.ReadLine();
        }
    }
}