As far as I know, the 666 is not always associating with the devil,,,,
And I don't agree with that the number is symbolize the devile,,,
I'm with the opinion which says that the number is invented by Metal Music Bands,,,
Consider an example, Iron Maiden, Him, Children of Bodom and Slipknot,,, and so on,,, they are into the number {666} in thier songs, gears ,,, etc.
And I entirly agree with Negative and Nihil,,,