This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A231005 #4 Nov 02 2013 23:39:52 %S A231005 0,1,3,6,8,9,11,14,15,17,18,19,20,22,23,26,27,28,29,31,32,34,35,37,38, %T A231005 40,41,43,44,45,46,49,50,52,53,54,55,57,58,60,61,63,64,66,67,68,69,70, %U A231005 71,72,73,74,75,76,77,78,80,81,83,84,86,87,89,90,91,92,94,95,98,99 %N A231005 Number of months after which a date can fall on the same day of the week, in the Gregorian calendar. %C A231005 In the Gregorian calendar, a non-century year is a leap year if and only if it is a multiple of 4 and a century year is a leap year if and only if it is a multiple of 400. %C A231005 Assuming this fact, this sequence is periodic with a period of 4800. %H A231005 Time And Date, <a href="http://www.timeanddate.com/calendar/repeating-month.html">Repeating Months</a> %H A231005 Time And Date, <a href="http://www.timeanddate.com/calendar/gregorian-calendar.html">Gregorian Calendar</a> %e A231005 1 belongs to this sequence because February 1, 2013 falls on the same day as March 1, 2013. %e A231005 3 belongs to this sequence because December 1, 2011 falls on the same day as March 1, 2012. %e A231005 6 belongs to this sequence because January 1, 2012 falls on the same day as July 1, 2012. %e A231005 8 belongs to this sequence because March 1, 2013 falls on the same day as November 1, 2013. %e A231005 9 belongs to this sequence because January 1, 2013 falls on the same day as October 1, 2013. %e A231005 11 belongs to this sequence because December 1, 2011 falls on the same day as November 1, 2012. %o A231005 (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(4800,i,(m[((i-1)%12)+1]+((5*((i-1)\48)+(((i-1)\12)%4)-((i-1)\1200)+((i-1)\4800)-!((i-1)%48)+!((i-1)%1200)-!((i-1)%4800)-!((i-2)%48)+!((i-2)%1200)-!((i-2)%4800))))%7);x=vector(4800,i,n[((i-1)%12)+1]+!((i-2)%48)-!((i-2)%1200)+!((i-2)%4800));for(p=0,4800,for(q=0,4800,if(y[(q%4800)+1]==y[((q+p)%4800)+1],print1(p", ");break))) %Y A231005 Cf. A230995-A231014. %Y A231005 Cf. A231010 (Julian calendar). %K A231005 nonn,easy %O A231005 0,3 %A A231005 _Aswini Vaidyanathan_, Nov 02 2013