Make a list of the prime numbers below a given limit

PrimeSieve.cs

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

namespace PrimeSieve
{
    class Program
    {
        static void Main(string[] args)
        {
            int number = 0;
            Console.WriteLine("Enter Limit...");
            string input = Console.ReadLine();
            while(!int.TryParse(input, out number))
            {
                Console.WriteLine("Not a recognised number, try again");
                input = Console.ReadLine();
            }

            List<int> primes = GetPrimes(number);

            Console.WriteLine("Primes below {0} are:", number);
            primes.ForEach(i => Console.Write("{0}\t", i));
            Console.WriteLine("\nPress any key to quit");
            Console.ReadLine();
        }

        public static List<int> GetPrimes(int number)
        {
            List<int> primes = new List<int>();
            if (number < 2) return primes;

            Dictionary<int, bool> numberdict = new Dictionary<int, bool>();
            for (int i = 3; i < number; i += 2)
            {
                numberdict[i] = true;
            }

            primes.Add(2);

            int testnumber = 3;
            float numbersqrt = (float)Math.Sqrt(number);
            while (testnumber < numbersqrt)
            {
                if (numberdict[testnumber])
                {
                    primes.Add(testnumber);
                    int multiplier = 2;
                    while (testnumber * multiplier < number)
                    {
                        numberdict[testnumber * multiplier] = false;
                        multiplier++;
                    }
                }
                testnumber += 2;
            }
            while (testnumber < number)
            {
                if (numberdict[testnumber])
                {
                    primes.Add(testnumber);
                }
                testnumber += 2;
            }

            return primes;
        }
    }
}