Fatto generale: 6939 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 6939 is a value of n for which 3n and 5n together use each digit exactly once.
Trivia: 6939 is an uninteresting number.
Data storica: December 30th is the day in 2006 that the Indonesian passenger ferry MV Senopati Nusantara sinks in a storm, resulting in at least 400 deaths.