Finding the Year’s Share in Day-of-Week Calculations

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The dominant part in the mental calculation of the day of the week for any given date is to determine the year share, that is, the contribution of the two-digit year part of the date. This paper describes a number of year share computation methods, some well-known and some new. The “Parity Minus 3” method, in particular, is a new alternative to the popular “Odd+11” method. The paper categorizes the methods of year share computation, and presents simpler proofs of their correctness than usually provided.

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researchers in the fields of games and puzzles, problems, mathmagic, mathematics and arts, math and fun with algorithms


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