666

From Infocentral

666 is the number of the devil in human numbers; it represents evil.

Like the Iron Maiden song "The number of the Beast" says:

"Woe to you, Oh Earth and Sea, for the Devil sends the beast with wrath, because he knows the time is short... Let him who hath understanding reckon the number of the beast for it is a human number, it's number is Six hundred and sixty six"