General fact: 797 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Mathematical fact: 797 is the number of functional graphs on 9 vertices.
Trivia: 797 is a boring number.
Historical date: March 7th is the day in 321 that Emperor Constantine I decrees that the dies Solis Invicti (sun-day) is the day of rest in the Empire.