general_fact: 4891 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
math_fact: 4891 is a narcissistic number in base 5.
trivia: 4891 is an unremarkable number.
historical_date: May 22nd is the day in 1968 that the nuclear-powered submarine the USS Scorpion sinks with 99 men aboard 400 miles southwest of the Azores.