Matt Parker per function from https://www.youtube.com/watch?v=Wim9WJeDTHQ written on common lisp

per.lsp

(defun div(n d)
  (multiple-value-bind (q r) (floor n d) q))

(defun per(n)
    (if (= n (rem n 10))
        (format t "~d~%" n)
        (progn
            (format t "~d->" n)
            (setq mul 1)
            (loop while (> n 0) do
                (progn
                    (setq d (rem n 10))
                    (setq mul (* mul d))
                    (setq n (div n 10))))
            (format t "~d~%" mul)
            (per mul))))

(per 277777788888899)
(bye)