Async without async

Async.cs

class Program
{
    static void Main(string[] args)
    {
        long number = 4278;
        var t = new Thread(() => FactorNumber(number, FactorizationDone));
        t.Start();
        t.Join();

        Console.ReadKey();
    }

    static void FactorizationDone(ISet<long> result)
    {
        Console.WriteLine("The work is done, the results are: {0}", string.Join(", ", result));
    }

    static void FactorNumber(long number, Action<ISet<long>> callback)
    {
        var dividers = new SortedSet<long>();
        for (long i = 1; i < number; i++)
        {
            if (number % i == 0)
                dividers.Add(i);
        }

        callback(dividers);
    }
}