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

https://zanessmartcolumn.brightsora.com/posts/why-is-4-avoided-in-some-languages-exploring-number-taboo-and-cultural-numerology

The number 7 is seen as lucky in slots and pop culture because it often represents good fortune and completeness. Classic slot machines frequently feature 777 as a winning combination