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In a period such as ours (1901 - 2099), in which there's a leap year every four years, there is a cycle of 28 years in which every type of non-leap year is repeated three times and every type of leap year occurs once, as the 4-year cycle of dates (1461 days) is incommensurate with the 7-day week.
We need to get the next seven leap years. Twenty-eight years, starting with 2010, would end with 2037, but year 2037 itself would not be needed as there would be two other years that are calendrically identical prior to that. But 2036 would be needed, as it's a leap year and only one of a given leap-year type occurs within they cycle. So 2036 is the year you'd complete your set.
From Enigma No. 1601, "Box of dates", by Bob Walker, New Scientist, 26 June 2010, page 29. |
