Maybe like thus ?
Least Common Multiple - Product of the prime factors
using Lee's pf prime_factor's:
(defun pf ( n / m p r ) ; LeeMac
(setq p 2)
(while (< 1 n)
(while (zerop (rem n p))
(setq r (cons p r)
n (/ n p)))
(if (< 1 (setq m (sqrt n))
(setq p (if (= p 2) 3 (+ 2 p))))
(setq r (cons n r)
n 0)
(while (and (<= p m)
(< 0 (rem n p)))
(setq p (+ 2 p)))))
(reverse r))
(defun ListLCM (l / pl fl)
(foreach a l
(setq pl (pf a))
(foreach f pl
(if (not (member f fl))
(setq fl (cons f fl)))))
(apply '* fl))
-David