Fait mathématique: 1684 is the number of multigraphs with 6 vertices and 9 edges.
Culture générale: 1684 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Date historique: August 10th is the day in 1270 that Yekuno Amlak takes the imperial throne of Ethiopia, restoring the Solomonic dynasty to power after a 100-year Zagwe interregnum.