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

https://wiki-nest.win/index.php/What_Does_Number_7_Mean_in_Games_Besides_Casinos%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