general_fact: 21706 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
math_fact: 21706 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
trivia: 21706 is an unremarkable number.
historical_date: June 5th is the day in 1989 that the Unknown Rebel halts the progress of a column of advancing tanks for over half an hour after the Tiananmen Square protests of 1989.