[jecel]

The Indy 500 was actually part of the official Formula 1 calendar from 1950 to 1960, though the two series diverged after that.

Some Indy features (refueling, changing tires even if they didn't have a puncture, safety cars) got adopted by F1 through the 1980s, specially as F1 started to lose audience to the American series in the early 1990s.