Indeed, there Apollo 18, Apollo 19, and Apollo 20 were manifested to fly at one time. But each of these missions was canceled due to congressional budget cuts and a waning public interest in voyages to the moon."
Link to Original Source
"Don't try to outweird me, three-eyes. I get stranger things than you free with my breakfast cereal." - Zaphod Beeblebrox in "Hithiker's Guide to the Galaxy"