[ncfqlksl] Ancient Prime Day

Let the start of the epoch be floor(exp(365.2425/2)) days before January 1, 2000.  This date in the extreme long past causes all prime days to currently occur with average spacing about half a year.  If a calendar year has multiple prime days, choose the first one as the Ancient Prime Day for the year.  (The average spacing of half a year was chosen to decrease the likelihood of two Ancient Prime Days occurring very close to each other around a New Year.)  If a year has no prime days, repeat the date of the last year that had a prime day, unless that year had multiple prime days, then use the next unused date, cycling through multiple times if necessary.

This is another idea for Modern computus.