The Number 7 is considered a lucky number in many societies. This may have many different origins. There are religious origins as in the seventh day is considered the Sabbath. Among the ancients, seven represented the seventh son of a seventh son would be born with special powers. The seventh daughter of a seventh daughter would be born with the gift of healing.
Of course today, the number 7 represents luck in virtually every casino in the world. 7 is a winning roll in Craps when there is no number chosen. 777 also stands for a winning spin on many slot machines.