public class PrimeToolBox
    {
        //internal list of prime numbers
        private List<int> thePrimeList;
        //set as read only
        public IReadOnlyList<int> ThePrimeList { get { return thePrimeList; } }
 
        /// <summary>
        /// Prime toolbox object w/ a list of primes from 2 - primesTo
        /// </summary>
        /// <param name="primeTo">Calculate list of primes to this number</param>
        public PrimeToolBox(int primesTo)
        {
            ChangePrimeList(primesTo);
        }
 
        /// <summary>
        /// Change the size of the internal list of primes
        /// </summary>
        /// <param name="primesTo">Updates the prime list from 2 - this number</param>
        public void ChangePrimeList(int primesTo)
        {
            thePrimeList = new List<int>();
            thePrimeList.Add(2);
            int limit = (primesTo - 3) / 2;
            bool[] sieve = new bool[limit]; //inits as false, for simplicity keep and treat as inverse
 
            for (int i = 0; i < limit; i++)
            {
                if (sieve[i] == true)//flipped
                { continue; }
                thePrimeList.Add(2 * i + 3);
                for (int j = ((2 * i + 6) * i + 3); j < limit; j += (2 * i + 3))
                {
                    sieve[j] = true;//flipped
                }
            }
        }
 
        /// <summary>
        /// Returns a list of a numbers Prime Factors
        /// </summary>
        /// <param name="number">to factor</param>
        /// <returns></returns>
        public List<int> GetPrimeFactors(int number)
        {
            List<int> tempFactors = new List<int>();
            foreach (int denominator in this.ThePrimeList.Where(i => i < (number / 2)))
            {
                while (number % denominator == 0)
                {
                    tempFactors.Add(denominator);
                    number = (number / denominator);
                }
            }
            //was it a prime? If so return its value
            if (number > 1) { tempFactors.Add(number); }
 
            return tempFactors;
        }
 
        /// <summary>
        /// Returns a numbers total divisors. Make sure the Prime list is large enough
        /// </summary>
        /// <param name="number"></param>
        /// <returns></returns>
        public int GetTotalDivisors(int number)
        {
            int totalDivisors = 1;
            int currentExponent = 1;
 
            foreach (int denominator in this.ThePrimeList.Where(i => i < number))
            {
                while (number % denominator == 0)
                {
                    number = number / denominator;
                    currentExponent += 1;
                }
                totalDivisors *= currentExponent;
                currentExponent = 1;
            }
            if (number > 1)
            {
                totalDivisors *= 2;
            }
            return totalDivisors;
        }
    }