Fatto generale: 21426 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 21426 is an unremarkable number.
Trivia: 21426 is an uninteresting number.
Data storica: August 29th is the day in 1982 that the synthetic chemical element Meitnerium, atomic number 109, is first synthesized at the Gesellschaft für Schwerionenforschung in Darmstadt, Germany.