Euler3

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Euler3
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine(GetFactors(600851475143).Where(x => IsPrime(x)).Max());
        }
        static bool IsPrime(int number)
        {

            if (number == 1) return false;
            if (number == 2) return true;

            var limit = Math.Ceiling(Math.Sqrt(number));

            for (int i = 2; i <= limit; ++i)
            {
                if (number % i == 0) return false;
            }
            return true;
        }

        static List<int> GetFactors(long number)
        {
            int currentFactor = 2;
            List<int> result = new List<int>();
            while (number > 1)
            {
                if (number % currentFactor == 0)
                {
                    result.Add(currentFactor);
                    number /= currentFactor;
                    currentFactor = 2;
                }
                else
                    currentFactor++;
            }
            return result;
        }
    }
}