Problem 7

(require 'calc-ext)
(defvar calc-command-flags nil)

(defun find-factor (num)
  (catch 'found
    (let ((i 2))
      (while (math-lessp (math-sub i 1) (math-floor (math-sqrt num)))
	(if (math-equal (math-mod num i) 0)
	    (throw 'found i)
	  (setq i (math-add i 1))) ))))

(let ((idx-searched (string-to-number (car argv)))
      (idx 0)
      (n 1)
      (prime))
  (while (< idx idx-searched)
    (setq n (1+ n))
    (if (not (find-factor n))
	(progn
	  (setq idx (1+ idx))
	  (setq prime n) )))
  (princ n)
  (princ "\n") )

メモ

• 割と実行に時間がかかった.
• 多倍長の必要はなかった.