Seven

Seven, a very cabalistic and used number through history, is considered as lucky number among other reasons for being the number of perfection.

God, the Bible says, created the Universe in 7 days. Thus 6 is the imperfect number, this is why 666 is the number of Satan or the Beast.

On dices, where seven is a winning number, to get a 7 you need one dice on 6 and a 1 on the opposite side on the other dice. All opposite side numbers adds to 7.