Fatto generale: 21189 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 21189 is a boring number.
Trivia: 21189 is an unremarkable number.
Data storica: January 4th is the day in 1976 that the Reavey and O'Dowd killings take place (part of The Troubles in Northern Ireland, United Kingdom).