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 A249404 Number of ISO 8601 weeks associated with the Gregorian year n. 1
 52, 52, 52, 52, 53, 52, 52, 52, 52, 53, 52, 52, 52, 52, 52, 53, 52, 52, 52, 52, 53, 52, 52, 52, 52, 52, 53, 52, 52, 52, 52, 52, 53, 52, 52, 52, 52, 53, 52, 52, 52, 52, 52, 53, 52, 52, 52, 52, 53, 52, 52, 52, 52, 52, 53, 52, 52, 52, 52, 52, 53, 52, 52, 52, 52, 53, 52, 52, 52 (list; graph; refs; listen; history; text; internal format)
 OFFSET 2000,1 COMMENTS There are 71 ISO 8601 53-week years per 400-year Gregorian cycle. The other years have 52 ISO 8601 weeks. These terms were calculated by using the .NET Framework's Calendar.GetWeekOfYear method with both CalendarWeekRule.FirstFourDayWeek and DayOfWeek.Monday specified for 12/28 of each year (as this date is always in the last week of an ISO 8601-week year). On the Gregorian Calendar, each 400-year cycle includes 97 leap years, giving a total of 400*365 + 97 = 146097 days, which is exactly 20871 weeks; this matches the total number of ISO 8601 weeks per 400-year cycle: 71*53 + (400-71)*52 = 20871. - Jon E. Schoenfield, Oct 30 2014 LINKS Rick L. Shepherd, Table of n, a(n) for n = 2000..2399 ISO, ISO 8601:2004 - Data elements and interchange formats -- Information interchange -- Representation of dates and times Microsoft Developer Network, CalendarWeekRule Enumeration Shawn Steele, ISO 8601 Week of Year Format in Microsoft .Net Wikipedia, ISO week date Wikipedia, Leap week calendar Wikipedia, Seven-day week Index entries for sequences related to calendars FORMULA a(n) = a(n - 400) for all n and n - 400 that are defined (proleptic) Gregorian calendar years. EXAMPLE a(2015) = 53 because Gregorian year 2015 has 53 associated ISO 8601 weeks (with week 1 beginning Monday, December 29, 2014). CROSSREFS Cf. A116386. Sequence in context: A126767 A143723 A252713 * A327374 A327109 A327108 Adjacent sequences: A249401 A249402 A249403 * A249405 A249406 A249407 KEYWORD nonn AUTHOR Rick L. Shepherd, Oct 27 2014 STATUS approved

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Last modified December 11 09:49 EST 2023. Contains 367722 sequences. (Running on oeis4.)