anchor.diff:          |> Seq.map (fun i -> (bestTo i (tree.Length - 1)))
           |> Seq.max
   
  -    let prob18result = (bestRoute tree18)
  +    let prob18result = bestRoute tree18
       printfn "Problem 18: %A" prob18result
   
       let tree67 = "59
  
positive.code: 30 11 85 31 34 71 13 48 05 14 44 03 19 67 23 73 19 57 06 90 94 72 57 69 81 62 59 68 88 57 55 69 49 13 07 87 97 80 89 05 71 05 05 26 38 40 16 62 45 99 18 38 98 24 21 26 62 74 69 04 85 57 77 35 58 67 91 79 79 57 86 28 66 34 72 51 76 78 36 95 63 90 08 78 47 63 45 31 22 70 52 48 79 94 15 77 61 67 68
  23 33 44 81 80 92 93 75 94 88 23 61 39 76 22 03 28 94 32 06 49 65 41 34 18 23 08 47 62 60 03 63 33 13 80 52 31 54 73 43 70 26 16 69 57 87 83 31 03 93 70 81 47 95 77 44 29 68 39 51 56 59 63 07 25 70 07 77 43 53 64 03 94 42 95 39 18 01 66 21 16 97 20 50 90 16 70 10 95 69 29 06 25 61 41 26 15 59 63 35"
  
      let prob67result = (bestRoute tree67)
      printfn "Problem 67: %A" prob67result
  
  //module Problem19 =
      
negative.code:     let isPrime (n : int) =
          if n % 2 = 0 then false
          else
              let root = int (sqrt (float n))
              seq {3..2..root} |> Seq.forall (fun i -> n % i <> 0)
  
      let num = 600851475143L
      let root = int (sqrt (float num))
      let largest =
          seq {2..root}
          |> Seq.filter (fun i -> num % (int64 i) = 0L)
  