Fatto matematico: 21945 is an uninteresting number.
Trivia: 21945 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Data storica: January 30th is the day in 1667 that the Polish-Lithuanian Commonwealth cedes Kiev, Smolensk, and left-bank Ukraine to the Tsardom of Russia in the Treaty of Andrusovo.