Doomsday rule

John Conway, inventor of the Doomsday algorithm.

A simple flowchart showing the Odd+11 method.

The Doomsday rule or Doomsday algorithm is a way of calculating the day of the week of a given date. It provides a perpetual calendar because the Gregorian calendar moves in cycles of 400 years.

This algorithm for mental calculation was devised by John Conway after drawing inspiration from Lewis Carroll's work on a perpetual calendar algorithm. It takes advantage of each year having a certain day of the week (the doomsday) upon which certain easy-to-remember dates fall; for example, 4/4, 6/6, 8/8, 10/10, 12/12, and the last day of February all occur on the same day of the week in any given year. Applying the Doomsday algorithm involves three steps:

单词	Doomsday rule
释义	Doomsday rule 英语百科 Doomsday rule The Doomsday rule or Doomsday algorithm is a way of calculating the day of the week of a given date. It provides a perpetual calendar because the Gregorian calendar moves in cycles of 400 years. This algorithm for mental calculation was devised by John Conway after drawing inspiration from Lewis Carroll's work on a perpetual calendar algorithm. It takes advantage of each year having a certain day of the week (the doomsday) upon which certain easy-to-remember dates fall; for example, 4/4, 6/6, 8/8, 10/10, 12/12, and the last day of February all occur on the same day of the week in any given year. Applying the Doomsday algorithm involves three steps:
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