using System;

public class Program

{

    public static bool IsPrime(int number)

{

    if (number <= 1) return false;

    if (number == 2) return true;

    if (number % 2 == 0) return false;

​

    var boundary = Sqrt(number);

​

    for (int i = 3; i <= boundary; i+=2)

        if (number % i == 0)

            return false;

​

    return true;        

}

    public static int Sqrt(int num) {  

        if (num == 0) { return 0; }  // Avoid zero divide  

        int n = (num / 2) + 1;       // Initial estimate, never low  

        int n1 = (n + (num / n)) / 2;  

        Console.WriteLine("n " + n);

        Console.WriteLine("n1 " + n1);

        while (n1 < n) {  

            n = n1;  

            n1 = (n + (num / n)) / 2;  

        } // end while  

                Console.WriteLine("n  after" + n);

​

        return n;  

    } // end Isqrt() 

    public static void Main()

    {

        int number = 47;

        Console.WriteLine("num " + number + " prime " + IsPrime(number));

    }

}