Syracuse sequence on Common Lisp

syracuse-cycle.lsp

(defvar *n* (read))
(defvar *counter* 0)
(do () ((= *n* 1) *n*)
    (setf *counter* (1+ *counter*))
    (format t "~d->~d~%"
         *n*
         (if (= (mod *n* 2) 0)
            (let ((n1 (/ *n* 2))) (setf *n* n1) n1)
            (let ((n1 (1+ (* *n* 3)))) (setf *n* n1) n1))))
(format t "Loops in ~d steps~%" *counter*)
(exit)

syracuse-recur.lsp

(defun syracuse(n)
    (if (= n 1)
        '(1)
        (if (= (mod n 2) 0)
            (cons n (syracuse (/ n 2)))
            (cons n (syracuse (1+ (* n 3)))))))
(format t "~A~%" (syracuse (read)))
(exit)