General fact: 11821 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Mathematical fact: 11821 is a boring number.
Trivia: 11821 is an uninteresting number.
Historical date: May 12th is the day in 2006 that Mass unrest by the Primeiro Comando da Capital begins in São Paulo (Brazil), leaving at least 150 dead.