FACTORS in Common Lisp using ITERATE

gistfile1.lisp

(defun factors (n)
  (iterate
    (with limit = (isqrt n))
    (for factor from 1 below limit)
    (for (values q r) = (floor n factor))
    (when (zerop r)
      (collect factor into lows)
      (collect q into highs))
    (finally (setf highs (reverse highs))
             (when (= n (* limit limit))
               (push limit highs))
             (return (nconc lows highs)))))