Parallel.For in C#

I am trying convert the following Collatz Conjecture algorithm from:

 public class CollatzConjexture
    {
        public static int Calculate(int StartIndex, int MaxSequence)
        {
            int ChainLength = 0;
            int key = 0;
            bool ContinuteCalulating = true;
            int LongestChain = 0;
            Int64 Remainder = 0;

            for (int i = StartIndex; i <= MaxSequence; i++)
            {
                ChainLength = 1;
                Remainder = i;
                ContinuteCalulating = true;

                while (ContinuteCalulating)
                {
                    Remainder = CalculateCollatzConjecture(Remainder);
                    if (Remainder == 1)
                        ContinuteCalulating = false;

                    ChainLength += 1;
                }

                if (ChainLength > LongestChain)
                {
                    LongestChain = ChainLength;
                    key = i;
                }
            }

            return key;
        }

        private static Int64 CalculateCollatzConjecture(Int64 Number)
        {
            if (Number % 2 == 0)
                return Number / 2;
            else
                return (3 * Number) + 1;
        }
    } 

To instead use the .NET 4.0 Parallel.For :

int ChainLength = 0;
            int key = 0;
            bool ContinuteCalulating = true;
            int LongestChain = 0;
            Int64 Remainder = 0;

            int[] nums = Enumerable.Range(1, 1500000).ToArray();
            long total = 0;

            // Use type parameter to make subtotal a long, not an int
            Parallel.For<int>(1, nums.Length, () => 1, (j, loop, subtotal) =>
            {
                Remainder = j;

                while (ContinuteCalulating)
                {
                    Remainder = CalculateCollatzConjecture(Remainder);
                    if (Remainder == 1)
                        ContinuteCalulating = false;

                    ChainLength += 1;
                }

                if (ChainLength > LongestChain)
                {
                    LongestChain = ChainLength;
                    key = j;
                }
                return key;


            },
                (x) => Interlocked.Add(ref key, x)
            );

I have a feeling I'm not too far from it, famous last words.

Thanks in advance.