OFFSET
1,1
COMMENTS
Gregorian calendar repeats after every 400 years because number of days in 400 years is 146097 which is a multiple of 7.
Non-century years are leap years if and only if they are multiples of 4 while century years are leap years if and only if they are multiples of 400.
43 occurrences in 400 years.
Months having Friday the 13th: May.
365 day ordinary year: 52 Sundays, 52 Mondays, 52 Tuesdays, 52 Wednesdays, 52 Thursdays, 52 Fridays, 53 Saturdays.
LINKS
Time and Date, The Gregorian calendar
Time and Date, 2011
Wikipedia, Gregorian calendar
Index entries for linear recurrences with constant coefficients, signature (1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, -1).
MATHEMATICA
Needs["Calendar`"]; Select[Range[1583, 2600], DayOfWeek[{#, 1, 1}, Calendar -> Gregorian] == Saturday && DaysBetween[{#, 1, 1}, {# + 1, 1, 1}, Calendar -> Gregorian] == 365 &, 50] (* T. D. Noe, Apr 22 2013 *)
Select[Range[1583, 2500], !LeapYearQ[{#}]&&DayName[{#, 1, 1}]==DayName[{#, 12, 31}]==Saturday&] (* Harvey P. Dale, Aug 14 2022, v9 or later *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Aswini Vaidyanathan, Apr 21 2013
STATUS
approved