Fait général: 1842 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fait mathématique: 1842 is the number of rooted trees with 11 vertices.
Culture générale: 1842 is a boring number.
Date historique: January 15th is the day in 1962 that the Derveni papyrus, Europe's oldest surviving manuscript dating to 340 BC, is found in northern Greece.