[chaostheory]

http://en.wikipedia.org/wiki/Japanese_superstitions

> There are several unlucky numbers in Japanese. Traditionally, 4 and 9 are unlucky. Four is sometimes pronounced shi, which is also the word for death. Nine is also sometimes pronounced ku, which can mean suffering... Because of these unlucky numbers, sometimes levels or rooms with 4 or 9 don't exist in hospitals or hotels, and particularly in the maternity section of a hospital,

I've never heard of 7 being an unlucky number for any culture. Then again someone can prove me wrong.