General fact: 21568 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Mathematical fact: 21568 is a boring number.
Trivia: 21568 is an unremarkable number.
Historical date: January 18th is the day in 2012 that SOPA (Stop Online Piracy Act) and PIPA (Protect IP Act) is opposed online on internet by Blackout (2012 Wikipedia blackout).