What is the relation between slot machines and the number 7?

double triple 7 slot machine-hi-IN V प्रिंट आधिकारिक वेबसाइट  डबल तिगुना 7 स्लॉट मशीन, एक

Triple Double Gems 3 Reel Progressive Jackpot Slot Gulf Coast The Slot Museum

double diamond free slot Lining Up Those Sevens! Double Jackpot Blazing 7s! I had some fun on this old school Double Jackpot slot machine at Excalibur!

double bubble slot game The Double Classic 7's is a newer S2000 slot machine Match 3 7's symbols to enable the Jackpot! Win on all 5 lines This Double Classic 7s is a 3 reel slot