Summing digits of factorials

test.lisp

(defun factorial (n)
  (defun i_factorial (k acc)
    (if (= 0 k)
      acc
      (i_factorial (- k 1) (* k acc))))
  (i_factorial n 1))

(defun digits (n)
  (defun i_digits (k acc)
    (if (= 0 k)
      acc
      (i_digits (truncate k 10) (cons (mod k 10) acc))))
  (i_digits n '()))

(defun digits_s (n)
  (mapcar
    #'(lambda (k) (parse-integer (string k))) 
    (coerce (write-to-string n) 'list)))

(format T "~D~%" 
        (time (reduce
                '+
                (mapcar
                  #'(lambda (n) 
                      (reduce 
                        '+ 
                        (digits_s (factorial n)))) 
                  '(1 12 123 1234 12345 123456)))))