Friday The 13th
From
Lawrence D?Oliveiro@3:633/10 to
All on Saturday, March 14, 2026 21:58:50
There are only 14 different calendars for any year in the Gregorian
system. There are seven possibilities for January 1st falling on each
day of the week, multiplied by two possibilities of the year being a
leap year or not.
Calendars for non-leap years recur at intervals of 6 or 11 years
(depending on the number of intervening leap years). Calendars for
leap years recur at intervals of 28 or 40 years.
Each possible calendar has its own set of dates which fall on Friday
the 13th. A year can have from 1 to 3 instances of Friday the 13th.
Listing the months for each year that contain a Friday the 13th, the possibilities are:
Non-leap years:
Jan, Oct (e.g. 2017)
Feb, Mar, Nov (e.g. 2026)
Apr, Jul (e.g. 2018)
May (e.g. 2022)
Jun (e.g. 2025)
Aug (e.g. 2021, 2027)
Sep, Dec (e.g. 2013)
Leap years:
Jan, Apr, Jul (e.g. 2012)
Feb, Aug (e.g. 2004)
Mar, Nov (e.g. 2020)
May (e.g. 2016)
Jun (e.g. 2008)
Sep, Dec (e.g. 2024)
Oct (e.g. 2000, 2028)
Note that every month occurs once, and only once, in each list.
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* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)