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 A231013 #4 Nov 02 2013 23:40:54 %S A231013 2,4,5,7,10,12,13,16,21,24,25,30,33,36,39,42,44,47,48,50,51,53,56,59, %T A231013 62,65,67,70,76,79,82,84,85,88,90,93,96,97,99,102,105,107,108,111,116, %U A231013 119,120,122,125,128,134,136,137,139,142,144,145,148,151,153,154,156,157,162 %N A231013 Number of months after which it is not possible to have a date falling on the same day of the week, in the Julian calendar. %C A231013 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 A231013 Assuming this fact, this sequence is periodic with a period of 336. %C A231013 This is the complement of A231010. %H A231013 Time And Date, <a href="http://www.timeanddate.com/calendar/repeating-month.html">Repeating Months</a> %H A231013 Time And Date, <a href="http://www.timeanddate.com/calendar/julian-calendar.html">Julian Calendar</a> %o A231013 (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));if(j==0,print1(p", "))) %Y A231013 Cf. A230995-A231014. %Y A231013 Cf. A231008 (Gregorian calendar). %K A231013 nonn,easy %O A231013 1,1 %A A231013 _Aswini Vaidyanathan_, Nov 02 2013