Advent of Code F# Day 10 : look-and-say

lookandsay.fsx

// "Elves Look, Elves Say" - Day 10 - Advent of Code http://adventofcode.com/day/10 #AdventOfCode
let lookAndSay(input : string array) = 
    input
    |> Array.fold (fun acc el -> 
           match acc with
           | [||] -> [|(1, el)|]
           | _ -> 
               let count, item = acc.[acc.Length - 1]
               if el = item then 
                   acc.[acc.Length - 1] <- (count + 1, el)
                   acc
               else [|(1, el)|] |> Array.append acc) Array.empty
    |> Array.map ( fun (count, el) -> [| (count |> string) ;el|] )
    |> Array.concat

let rec iterate (numOfIterations : int) (count : int) (input : string array) = 
    if count = numOfIterations - 1 then (lookAndSay input)
    else lookAndSay input |> iterate (numOfIterations) (count + 1)

Environment : MacBook Pro | Yosemite | Xamarin Studio 5.10.1| F# Interactive for F# 4.0 (Open Source Edition)
Part One 40 iterations
Input : 1113222113
Length (Answer) : 252594

Evaluated In : 192830 miliseconds (3.21 minutes)

50 iterations was run on Windows because on MacBook Pro mono-sgen CPU usage was around 105%

Environment : HP Z1 Workstation | Windows 10 | Visual Studio 2013 | Microsoft's F# Interactive implementation 12.????
Part Two 50 iterations
Input : 1113222113
Length (Answer) : 3579328

Evaluated In : 39142510 miliseconds (10.9 hours)