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.

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

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 A352908

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