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A090651 Perpetual calendar sequence: There are 14 basic year calendars, 7 for normal years and 7 for leap years. This sequence identifies the calendars for years 1901 through 2099, when it reinitializes because 2100 is not a leap year. 2
3, 4, 5, 13, 1, 2, 3, 11, 6, 7, 1, 9, 4, 5, 6, 14, 2, 3, 4, 12, 7, 1, 2, 10, 5, 6, 7, 8, 3, 4, 5, 13, 1, 2, 3, 11, 6, 7, 1, 9, 4, 5, 6, 14, 2, 3, 4, 12, 7, 1, 2, 10, 5, 6, 7, 8, 3, 4, 5, 13, 1, 2, 3, 11, 6, 7, 1, 9, 4, 5, 6, 14, 2, 3, 4, 12, 7, 1, 2, 10, 5, 6, 7, 8, 3, 4, 5, 13, 1, 2, 3, 11, 6, 7, 1, 9, 4 (list; graph; refs; listen; history; text; internal format)
OFFSET

1901,1

COMMENTS

2000 was a leap year, so no reinitializing was needed.

Calendars are continuous so they roll from Dec 31 to Jan 01. The intercalation of the leap years causes the unusual sequence.

a(n) = 1 for years starting on a Sunday, 2 for years starting on a Monday, so on to 7; 8 for leap years starting on a Sunday, 9 for leap years starting on Monday, so on to 14. - Alonso del Arte, Nov 02 2004

REFERENCES

World Almanac 2003, Perpetual calendar on pages 647-648.

LINKS

Table of n, a(n) for n=1901..1997.

Index entries for sequences related to calendars

EXAMPLE

a(2003) = 4 because 2003 is a year starting on a Wednesday.

a(2004) = 5 because 2004 is a leap year starting on a Thursday.

CROSSREFS

Sequence in context: A280308 A289121 A060738 * A242497 A062201 A211518

Adjacent sequences:  A090648 A090649 A090650 * A090652 A090653 A090654

KEYWORD

nonn

AUTHOR

Brendan Sullivan (bsulliva(AT)austarnet.com.au), Dec 13 2003

EXTENSIONS

More terms from Ray Chandler, Dec 23 2003

STATUS

approved

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Last modified November 12 22:10 EST 2019. Contains 329079 sequences. (Running on oeis4.)