let select_fft_domain n =
    let rec powerset = function
      | [] -> [[]]
      | x :: xs ->
          let ps = powerset xs in
          List.concat [ps; List.map (fun ss -> x :: ss) ps]
    in
    let rec multiply_by_two n target pow_two =
      if n >= target then pow_two
      else multiply_by_two (2 * n) target (2 * pow_two)
    in
    let start =
      powerset [3; 11; 19]
      |> List.map (fun l ->
             let prod1 = List.fold_left ( * ) 1 l in
             let prod2 = multiply_by_two prod1 n 1 in
             let factors = prod2 :: l in
             (factors, List.fold_left ( * ) 1 factors))
    in
    List.fold_left
      (fun e acc -> if snd e < snd acc then e else acc)
      (List.hd start)
      start