This article is from the Calendars FAQ, by Claus Tondering claus@tondering.dk with numerous contributions by others.
A year is a leap year if the number 'year mod 19' is one of the
following: 0, 3, 6, 8, 11, 14, or 17.
The value for year in this formula is the "Anno Mundi" described in
section 3.8.
 
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