Project Euler Problem12 Too slow T_T

euler-12-slow.lisp

(defun sum-n (n)
  (if (= n 1)
	  1
	(+ n (sum (- n 1)))))

(defun check-div (num)
  (labels ((check-div-r (n k)
		   (if (= k 1)
			   1
			   (if (integerp (/ n k))
				   (1+ (check-div-r n (1- k)))
				   (check-div-r n (1- k))))))
	(check-div-r num num)))

(defun prob-12 (num)
  (do ((i 1 (1+ i)) (result 0))
	  ((> result num) (format t  "ans: ~A~%" (sum-n (1- i))))
	(setq result (check-div (sum-n i)))
	))

(time (prob-12 500))  ;; 時間がかかりすぎてとけましぇん(´・ω・`)