(progn
  (defun collatz-aux (n)
    (if (evenp n)
        (/ n 2)
      (+ (* 3 n) 1)))

  (defun collatz-list(n, li)
    (let* ((col (collatz-aux n)))
      (format "%d" col)
      (if (= col 1)
          li
        (collatz-list col (cons col li)))))

  (format t "~A" (collatz-list 3 ())))