Fatto generale: 21478 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 21478 is a boring number.
Trivia: 21478 is an unremarkable number.
Data storica: October 20th is the day in 1962 that China launches simultaneous offensives in Ladakh and across the McMahon Line, beginning the Sino-Indian War.