general_fact: 21303 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
math_fact: 21303 is an uninteresting number.
trivia: 21303 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
historical_date: April 28th is the day in 357 that Emperor Constantius II enters Rome for the first time to celebrate his victory over Magnus Magnentius.