General fact: 21136 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Mathematical fact: 21136 is an unremarkable number.
Trivia: 21136 is an uninteresting number.
Historical date: November 12th is the day in 1970 that the 1970 Bhola cyclone makes landfall on the coast of East Pakistan becoming the deadliest tropical cyclone in history.