using System;
using System.Collections.Generic;

namespace ConsoleApplication1
{
    class Program
    {
        

        /// <summary>
        ///  get the prime factors of <paramref name="value"/>
        /// </summary>
        /// <param name="value">the value to get prime factors of</param>
        /// <returns>prime factors stored in a list</returns>
        static List<uint> GetFactors(uint value)
        {
            List<uint> factors = new List<uint>();  // list of factors to return
            List<uint> primes = new List<uint>();   // prime numbers encountered
            uint k = 2; // initial prime number
            primes.Add(k);  // load the first prime number to the prime list

            while (true)
            {
                if (value == k)
                {
                    factors.Add(k);
                    break;
                }
                else if (value % k == 0)
                {
                    factors.Add(k);
                    value /= k;
                }
                else
                {
                    bool isPrime;
                    do
                    {
                        k+=2;
                        isPrime = true;
                        foreach (uint prime in primes)
                        {
                            // k is divisible by 'prime'
                            // k is not a prime number
                            if (k % prime == 0)
                            {
                                isPrime = false;
                                break;
                            }
                            if (prime > Math.Sqrt(k))
                            {   // no need to check other numbers
                                break;
                            }
                        }
                    } while (!isPrime);
                    primes.Add(k);  // add k to the list
                }
            }

            return factors;
        }

        static void Main(string[] args)
        {
            Console.Write("Input a number: ");
            string input = Console.ReadLine();
            uint value = Convert.ToUInt32(input);
            List<uint> factors = GetFactors(value);
            Console.Write("{0} = ", value);
            for (int i = 0; i < factors.Count - 1; i++)
            {
                Console.Write("{0} * ", factors[i]);    // print the factors except for the last
            }
            Console.WriteLine("{0}", factors[factors.Count - 1]);   // print the last factor
        }
    }
}

------解决方案--------------------
C# code

static List<int> GetPrimes(int m)
{
    List<int> primes = new List<int>();

    for (int i = 2; i <= m; )
    {
        if (IsPrime(i) && m % i == 0)
        {
            primes.Add(i);
            m /= i;
        }
        else
        {
            i++;
        }
    }

    return primes;
}
static bool IsPrime(int m)
{
    if (m == 2) return true;
    if (m == 1 || m % 2 == 0