A101944 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.

687, 685, 685, 687, 684, 688, 684

Offset

1,1

Comments

Friday the thirteenth appears more often than any other day.

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

References

Alfred S. Posamentier, Math Charmers, Tantalizing Tidbits for the Mind, Prometheus Books, NY, 2003, page 230.

Links

Table of n, a(n) for n=1..7.

E. G. Richards, Mapping Time, The Calendar and its History, Oxford University Press, Great Clarendon Street, Oxford OX2 6DP, Reprinted 1999 (with corrections).

Wikipedia, Gregorian calendar

Index entries for sequences related to calendars

Mathematica

(* 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}]

Crossrefs

Sequence in context: A222751 A234817 A203459 * A045150 A296811 A252642

Adjacent sequences: A101941 A101942 A101943 * A101945 A101946 A101947

Keyword

fini,full,nonn,dumb

Author

Robert G. Wilson v, Jan 28 2005

Status

approved