Fatto generale: 2156 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 2156 is the number of different positions in Connect Four after 5 moves.
Trivia: 2156 is an unremarkable number.
Data storica: November 25th is the day in 1947 that New Zealand ratifies the Statute of Westminster and thus becomes independent of legislative control by the United Kingdom.