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 A231008 #4 Nov 02 2013 23:40:19 %S A231008 2,4,5,7,10,12,13,16,21,24,25,30,33,36,39,42,47,48,51,56,59,62,65,79, %T A231008 82,85,88,93,96,97,102,105,108,111,119,120,128,134,137,139,142,148, %U A231008 151,154,156,157,165,168,174,180,183,188,191,192,194,197,200,211,214,220,228,229 %N A231008 Number of months after which it is not possible to have a date falling on the same day of the week, in the Gregorian calendar. %C A231008 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 A231008 Assuming this fact, this sequence is periodic with a period of 4800. %C A231008 This is the complement of A231005. %H A231008 Time And Date, <a href="http://www.timeanddate.com/calendar/repeating-month.html">Repeating Months</a> %H A231008 Time And Date, <a href="http://www.timeanddate.com/calendar/gregorian-calendar.html">Gregorian Calendar</a> %o A231008 (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,j=0;for(q=0,4800,if(y[(q%4800)+1]==y[((q+p)%4800)+1],j=1;break));if(j==0,print1(p", "))) %Y A231008 Cf. A230995-A231014. %Y A231008 Cf. A231013 (Julian calendar). %K A231008 nonn,easy %O A231008 1,1 %A A231008 _Aswini Vaidyanathan_, Nov 02 2013