Unlucky Thirteenths
The Gregorian calendar repeats exactly every 400 years (146 097 days, which is a whole number of weeks). Over one complete 400-year cycle, on how many dates does the 13th of a month fall on a Friday? Give an integer.
Related problems & prerequisites
Worth solving first
- The Quarter-Turn Hands 3.0/10
Source: Friday-the-13th frequency in the Gregorian calendar is a well-known calendar fact; this counting question written for AxiomIQ.