An alternate calendar system briefly used by republican France. It had 360 days per year with 5 or 6 “intercalary” or leap days between years. It had 12 months of 30 days, which were comprised by 3 weeks of 10 days. Every day of the year had a unique name: a common plant, animal, mineral, or tool/equipment (ie January 31 was “Broccoli” and May 4 was “Silkworm”).
YSK because it’s an interesting alternative to the Gregorian calendar and the occasionally-proposed 13 month calendar.
Though it did have some problems such as starting in late September (very unusual for a calendar) and not having a robust leap-year system.
13! A prime number indivisible into anything. Ugh!
13! is definitely not a prime number, but it’s too large to be useful in this context (I know, I know, you didn’t actually MEAN 13-factorial, but I’ve studied enough maths that I couldn’t help it).
I’ve seen people object to a 13 month calendar based solely on the idea that you can’t divide the year into quarters. But it’s actually really easy to remember. A quarter is 13 weeks, or 3 months and 1 week. So Q1 ends a week after month three, Q2 ends 2 weeks after month six, Q3 ends 3 weeks after month nine, and q4 ends after month 13 aka the end of the year. And since the calendar doesn’t change, you don’t even need to remember it, just mark the quarter ends once and you’re done forever.
Just compare that to the unnecessary complexity of the Gregorian calendar and the effort it takes to remember basically anything that changes from year to year, or what day of the week any given date or holiday falls on, or even just which months have 30 days and which have 31.
Fine! Four months of thirteen weeks, and no more complaining!