The Memetic Number is basically a number that, aside from being an Arc Number, is so ingrained into the audience's mind that they often use it idiomatically on other media (e.g. the Internet), thereby giving it memetic status. Furthermore, it is taken beyond the specific media into general pop culture, much to the point that were it not for helpful archiving from sites like The Other Wiki the original reference would be lost---something an Arc Number would envy. It also helps if the number is currently associated with a meme.