Async with async, CPU bound

Async.cs

class Program
{
    static void Main(string[] args)
    {
        StartWork();
        Console.WriteLine("Processing is happening right now..");
        Console.ReadKey();
    }

    static async Task StartWork()
    {
        long number = 4278;
        var result = await Task.Run(() => FactorNumber(number));
        Console.WriteLine("The work is done, the results are: {0}", string.Join(", ", result));
    }

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

        return dividers;
    }
}