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

https://victor-wiki.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 partly because of classic reel symbols like 777, which often signal a big win. It’s also tied to the seven-day week, making it feel familiar and lucky to many people playing games like those on MrQ.