I think there should be an achievement for x number of achievements. Keeping with the prime numbers, there could be three of these:
61 - Cheevo Down
101 - Mmmmm... Cheevoliscious!
239 - Achievement "Glitch of the Night" (play on Achievement Whore form the Xbox community)
There could, of course, be additional levels or tweaks to the number depending on the number of achievements in the game at the time it was implemented.