let trialDivision (k:bigint) : bigint array =
    let n = abs(k)

    if n.IsZero || n.IsOne || n.Equals(2) then
        [|k; bigint.One|]

    elif n.IsEven then
        [|bigint.Divide(k, bigint 2); bigint 2|]

    else
        let rec iterate (dividend:bigint) (divisor:bigint) : bigint =
            if bigint.Remainder(dividend, divisor).IsZero then
                divisor
            else
                if bigint.Pow(divisor, 2).CompareTo(dividend) > 0 then
                    dividend
                else
                    iterate dividend (bigint.Add(divisor, bigint 2))

        let factor = iterate n (bigint 3)
        [|bigint.Divide(k, factor); factor|]




let AsyncTrialDivision(k:bigint) : bigint array =
    let n = abs(k)

    if n.IsZero || n.IsOne || n.Equals(2) then
        [|k; bigint.One|]

    elif n.IsEven then
        [|bigint.Divide(k, bigint 2); bigint 2|]

    else
        let factor = ref k

        let parallelOption = new ParallelOptions()
        parallelOption.MaxDegreeOfParallelism <- 4;

        Parallel.ForEach(seq { for divisor in bigint 3 .. bigint 2 .. n -> divisor }, parallelOption, (fun (divisor:bigint) (loopState:ParallelLoopState) ->
            if bigint.Remainder(n, divisor).IsZero then
                factor := divisor
                loopState.Stop()
        ))
        |> ignore

        [|bigint.Divide(k, !factor); !factor|]