cp's OEIS Frontend

A231239 Number of months after which either it is not possible to have a date to fall on the same day of the week, or that it is possible to have a date falling on the same day of the week and the two months have the same number of days, in the Julian calendar.

%I A231239 #4 Nov 13 2013 15:18:25
%S A231239 0,2,3,4,5,6,7,8,9,10,12,13,14,15,16,17,18,20,21,22,23,24,25,26,29,30,
%T A231239 31,32,33,34,35,36,37,38,39,40,42,43,44,46,47,48,50,51,52,53,54,55,56,
%U A231239 57,59,60,62,63,64,65,67,68,69,70,72,75,76,77,78,79,80,81,82,84,85,86,88,89
%N A231239 Number of months after which either it is not possible to have a date to fall on the same day of the week, or that it is possible to have a date falling on the same day of the week and the two months have the same number of days, in the Julian calendar.
%C A231239 In the Julian calendar, a year is a leap year if and only if it is a multiple of 4 and all century years are leap years.
%C A231239 Assuming this fact, this sequence is periodic with a period of 336.
%C A231239 This is the complement of A231012.
%H A231239 Time And Date, <a href="http://www.timeanddate.com/calendar/repeating-month.html">Repeating Months</a>
%H A231239 Time And Date, <a href="http://www.timeanddate.com/calendar/julian-calendar.html">Julian Calendar</a>
%o A231239 (PARI) m=[0,3,3,6,1,4,6,2,5,0,3,5];n=[31,28,31,30,31,30,31,31,30,31,30,31];y=vector(336,i,(m[((i-1)%12)+1]+((5*((i-1)\48)+(((i-1)\12)%4)-!((i-1)%48)-!((i-2)%48))))%7);x=vector(336,i,n[((i-1)%12)+1]+!((i-2)%48));for(p=0,336,j=0;for(q=0,336,if(y[(q%336)+1]==y[((q+p)%336)+1],j=1;break));for(q=0,336,if(y[(q%336)+1]==y[((q+p)%336)+1]&&x[(q%336)+1]==x[((q+p)%336)+1],j=2;break));if(j!=1,print1(p", ")))
%Y A231239 Cf. A230995-A231014, A231236-A231239.
%Y A231239 Cf. A231238 (Gregorian calendar).
%K A231239 nonn,easy
%O A231239 1,2
%A A231239 _Aswini Vaidyanathan_, Nov 06 2013