Fatto generale: 20411 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 20411 is an uninteresting number.
Trivia: 20411 is an uninteresting number.
Data storica: November 18th is the day in 1947 that the Ballantyne's Department Store fire in Christchurch, New Zealand, kills 41; it is the worst fire disaster in the history of New Zealand.