let multiplyOthers (input : int[]) = 

  let front = Array.zeroCreate input.Length

  let rear  = Array.zeroCreate input.Length

  front.[0] <- 1

  rear.[input.Length-1] <- 1

​

  for i = 1 to input.Length-1 do

    front.[i] <- front.[i-1] * input.[i-1]

​

  // start from second to last element

  for i in input.Length-2 .. -1 .. 0 do

    rear.[i] <- rear.[i+1] * input.[i+1]

​

  Seq.zip front rear 

  |> Seq.map (fun (f, r) -> f * r)

  |> Seq.toArray

​

multiplyOthers [| 2;3;1;4|] |> printfn "%A"