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%I #13 May 03 2022 23:35:13
%S 687,685,685,687,684,688,684
%N Number of months in a 400-year cycle that have the thirteenth day of the month fall on the n-th day of the week, beginning with Sunday.
%C Friday the thirteenth appears more often than any other day.
%C In the cycle of 400 Gregorian years there are 303 regular years with 365 days, and 97 leap years with 366 days, so the total number of days is 303*365 + 97*366 = 146097, which is divisible by 7. - _Amiram Eldar_, Apr 29 2022
%D Alfred S. Posamentier, Math Charmers, Tantalizing Tidbits for the Mind, Prometheus Books, NY, 2003, page 230.
%H E. G. Richards, <a href="http://www.users.zetnet.co.uk/egrichards/book.htm">Mapping Time, The Calendar and its History</a>, Oxford University Press, Great Clarendon Street, Oxford OX2 6DP, Reprinted 1999 (with corrections).
%H Wikipedia, <a href="https://en.wikipedia.org/wiki/Gregorian_calendar">Gregorian calendar</a>
%H <a href="/index/Ca#calendar">Index entries for sequences related to calendars</a>
%t (* first do *) Needs["Miscellaneous`Calendar`"] (* then *) t = Flatten[ Table[ DayOfWeek[{y, m, 13}], {y, 2000, 2399}, {m, 12}]]; d = Table[ DayOfWeek[{2006, 1, d}], {d, 1, 7}]; Table[ Count[t, d[[n]]], {n, 1, 7}]
%K fini,full,nonn,dumb
%O 1,1
%A _Robert G. Wilson v_, Jan 28 2005
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