Gregorian leap year rule
About the Gregorian leap year rule
A Gregorian year is a leap year if it is divisible by 4, except century years, which must be divisible by 400. So 1600 and 2000 were leap years but 1700, 1800 and 1900 were not, and 2100 will not be. The 400-year cycle contains exactly 146,097 days, which is 20,871 weeks, so the calendar repeats weekdays every 400 years.
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