general_fact: 6723 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
math_fact: 6723 is a value of n for which 3n and 8n together use each digit exactly once.
trivia: 6723 is an unremarkable number.
historical_date: May 28th is the day in 1995 that the Russian town of Neftegorsk is hit by a 7.6 magnitude earthquake that kills at least 2,000 people, half of the total population.