using System;

using System.Linq;

public class Program

{

    public static void Main(string[] args) {

        Console.Write("Enter Number: ");

        Int64 n = Convert.ToInt64(Console.ReadLine());

        Console.WriteLine("Start Time: " + DateTime.Now.ToString("HH:mm:ss.ffffff"));

        Console.WriteLine("Number, Factors");

        HomePrime(n);

        Console.WriteLine("End Time: " + DateTime.Now.ToString("HH:mm:ss.ffffff"));

        Console.ReadLine();

    }

    public static void HomePrime(Int64 num) {

        string s = FindFactors(num);

        if (CheckPrime(num,s) == true) {

            Console.WriteLine("{0} is prime", num);

        } else {

            Console.WriteLine("{0}, {1}", num, s);

            HomePrime(Convert.ToInt64(RemSp(s)));

        }

    }

    public static string FindFactors(Int64 num) {

        Int64 n, r, t = num;

        string f = "";

        for (n = num; n >= 2; n--) {

            r = CalcP(n, t);

            if (r != 0) {

                f = f + " " + r.ToString();

                t = n / r;

                n = n / r + 1;

            }

        }

        return f;

    }

    public static Int64 CalcP(Int64 num, Int64 tot) {

        for (Int64 i = 2; i <= tot; i++) {

            if (num % i == 0) {

                return i;

            } 

        }

        return 0;

    }

    public static string RemSp(string str) {

        return new string(str.ToCharArray().Where(c => !Char.IsWhiteSpace(c)).ToArray());

    }

    public static bool CheckPrime(Int64 num, string s) {

        if (s == "") {

            return false;

        } else if (num == Convert.ToInt64(RemSp(s))) {

            return true;

        }

        return false;

    }

​

}