Fatto generale: 681 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 681 is an uninteresting number.
Trivia: 681 is an uninteresting number.
Data storica: November 11th is the day in 1921 that the Tomb of the Unknowns is dedicated by US President Warren G. Harding at Arlington National Cemetery.