The number 7 is seen as lucky in slots and pop culture partly because classic...

https://sierra-wiki.win/index.php/What_Does_HISTORY.com_Say_About_Famous_Numbers_in_Pop_Culture%3F

The number 7 is seen as lucky in slots and pop culture partly because classic reels often feature triple 7s (777) as a big win symbol. It also ties into everyday life, like the seven-day week, making it feel familiar and lucky