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

https://blogfreely.net/teresa-long85/why-are-slot-symbols-designed-to-be-readable-on-small-screens

The number 7 is seen as lucky in slots and pop culture partly because classic slot machines often feature 777 as a big win symbol. It also connects to the idea of a seven-day week, symbolizing completeness and good fortune