general_fact: 28 is the number of days in the average human menstrual cycle.
math_fact: 28 is a harmonic divisor number, a happy number, a triangular number, a hexagonal number, and a centered nonagonal number.
trivia: 28 is the number of days the curing time of concrete is classically considered to be.
historical_date: January 28th is the day in 1724 that the Russian Academy of Sciences is founded in St. Petersburg by Peter the Great, and implemented by Senate decree.