Why is the number 7 so significant in Islam?

777 is God's number and a lot of tradition surrounds using variances of that. With islam a majority of their customs were taken from the many pagan religions they swallowed up as Muhammad conquered the lands, such as all that dancing around in Mecca predates islam and the black stone representing the moon god allah,(from which they get their name for their god) in the Kaaba is still worshiped.