for (int i = 0; i < 20; i += 2)


public IEnumerable<int> SteppedIntegerList(int startIndex,
            int endEndex, int stepSize)
{
        for (int i = startIndex; i < endEndex; i += stepSize)
    {
        yield return i;
    }
}


Parallel.ForEach(SteppedIntegerList(0, 20, 2), index =>
{

    Console.WriteLine("Index value: {0}", index);
});