The number 7 is seen as lucky in slots and pop culture because it’s often...

https://wiki-mixer.win/index.php/How_Do_Slot_Developers_Decide_Which_Symbols_Pay_More%3F

The number 7 is seen as lucky in slots and pop culture because it’s often linked to good fortune and completeness, like the seven-day week. In classic slot machines, hitting triple 7s (777) usually means a big win