general_fact: 857 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
math_fact: 857 is a value of n for which f(n) = f(n-1) + f(n-2).
trivia: 857 is an unremarkable number.
historical_date: May 6th is the day in 1536 that the Siege of Cuzco commences, in which Incan forces attempt to retake the city from Cuzco from the Spanish.