A090651 - OEIS

%I #8 Oct 12 2012 14:38:23

%S 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,

%T 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,

%U 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

%N 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.

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

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

%C 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

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

%H <a href="/index/Ca#calendar">Index entries for sequences related to calendars</a>

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

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

%K nonn

%O 1901,1

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

%E More terms from _Ray Chandler_, Dec 23 2003