Friday thirteen come on Friday this month
Somewhere or other I recently mentioned having heard that, because the Gregorian calendar cycle of 400 years is a multiple of 7 days, the 13th of the month is not evenly distributed and falls more often on Friday than on any other day of the week; but I had not done the math myself and did not have the numbers. Now I’ve done it but can’t remember where to post the followup!
Post it here! 🙂