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

https://marcossmartchat.image-perth.org/why-are-there-seven-wonders-of-the-ancient-world-and-not-eight

The number 7 is seen as lucky in slots and pop culture partly because of the classic "777" jackpot symbol on slot machines. It also connects to the seven-day week, which has long been important in many cultures