General fact: 21622 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Mathematical fact: 21622 is an uninteresting number.
Trivia: 21622 is an unremarkable number.
Historical date: March 13th is the day in 1988 that the Seikan Tunnel, the longest undersea tunnel in the world, opens between Aomori and Hakodate, Japan.