Fatto generale: 678 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 678 is a member of the Fibonacci-type sequence starting with 1 and 7.
Trivia: 678 is an unremarkable number.
Data storica: November 8th is the day in 1973 that the right ear of John Paul Getty III is delivered to a newspaper together with a ransom note, convincing his father to pay 2.9 million USD.