Lucky Seven/Lucky Number Seven is also just a common phrase in American culture. There’s even a Wikipedia page of things called Lucky [Number] Seven. https://en.m.wikipedia.org/wiki/Lucky_7

Some sustain that 7 is the God's number, stemming from "God created the world in seven days"[1]

Also, _"According to some, 777 represents the threefold perfection of the Trinity"_ [2]

[1] https://www.wikihow.com/What-Does-the-Number-7-Mean-in-the-B...

[2] https://en.wikipedia.org/wiki/777_(number)

“Lucky Number 7” is a common phrase, there was even a popular movie that played on this, “Lucky Number Slevin” (https://m.imdb.com/title/tt0425210/). It’s one of the first numbers I’d think of as a “lucky number.”