gistfile1.fs

let maxCollazSeqLength (x:int64,y:int64) = 
  let x',y' = System.Math.Min(x,y), System.Math.Max(x,y)

  seq[x'..y'] 
  |> Seq.fold (fun max x -> 
                    let r = collatzSeqLength x
                    if r > max then r else max) 0L