Fatto matematico: 7789 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Trivia: 7789 is an unremarkable number.
Data storica: April 28th is the day in 1947 that Thor Heyerdahl and five crew mates set out from Peru on the Kon-Tiki to prove that Peruvian natives could have settled Polynesia.