Fatto matematico: 1691 is the number of multigraphs with 5 vertices and 11 edges.
Trivia: 1691 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Data storica: August 17th is the day in 1945 that Sukarno and Mohammad Hatta proclaim the independence of Indonesia, igniting the Indonesian National Revolution against the Dutch Empire.