The cycle of the Gregorian Calendar is 400 years, encompassing exactly 146,097 days. In the Gregorian Calendar there are exactly 97 leap years every 400 years or 97 in 146,097 days. Century years divisible by 400 are not leap years. 1700, 1800, and 1900 were not leap years, 1600 and 2000 were. Since 146,097 is divisible by 7 (just a pure coincidence) the days of the week fall on the same calendar date every 400 years, though, of course, calendar years repeat the same date patterns (there are only 14 possible calendars) somewhat irregularly in between.
Unfortunately, 97 does not divide 146,097, and since 97 is prime they do not share any prime factors, so 97 times in 146,097 is about as good as you can get with integer divisors.
Same as once every 1506 and 15/97ths of a day.
Thanks,- I was looking at just any given 4 year window
Interesting as it goes longer
Hmmmmm
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