Oops.

18 = 3*3*2, 46 = 2*23, LCM(18,46) = 3*3*2*23 = 414. 414/46 = 9. Incidentally, the shorcut for all of this is to take the set of unique terms and eliminate the terms from the chainring. So LCM(18,46) = 3*3*2*23. Drop the 2*23 and you get 3*3 = 9, the result of LCM(18,46)/46.