let rec calc ai num n acc =
    if n = 0 then acc
    else
      let next = ai - 1.0 - 1.0 / (sqrt num)
      if ai < 0.0 then calc next (num + 1.0) (n-1) (ai::acc)
      else calc next (num + 1.0) n acc

printf "%A" <| calc 1000.0 1.0 5 []