Fatto generale: 20391 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 20391 is an unremarkable number.
Trivia: 20391 is an unremarkable number.
Data storica: October 29th is the day in 1998 that ATSC HDTV broadcasting in the United States is inaugurated with the launch of STS-95 space shuttle mission.