math_fact: 4615 is a value of n for which s(f(n)) = 2s(n).
trivia: 4615 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
historical_date: August 19th is the day in 2003 that a car-bomb attack on United Nations headquarters in Iraq kills the agency's top envoy Sergio Vieira de Mello and 21 other employees.