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

Author

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

Keywords

• nonn

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

Examples

			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.
		

References

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

Links

• Index entries for sequences related to calendars

Extensions

More terms from Ray Chandler, Dec 23 2003