euler3.lisp

(let* ((target 600851475143)  ;; number to factorize
       (n (floor (sqrt target)))  ;; size of sieve
       )
  (loop named outer
     with arr = (make-array n :initial-element nil)
     for i from 2 below n 
     unless (aref arr i)
     do (loop for j from i below n by i do (setf (aref arr j) i))
       (loop while (zerop (mod target i))
          do (format t "~a ~a~%" target i)
          if (= target i) do (return-from outer target) else do (setf target (/ target i)))))