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 A231003 #8 Jun 04 2024 10:52:04 %S A231003 1,2,3,4,7,8,9,10,12,13,14,15,16,18,19,20,21,24,25,26,27,29,30,31,32, %T A231003 35,36,37,38,40,41,42,43,44,46,47,48,49,52,53,54,55,57,58,59,60,63,64, %U A231003 65,66,68,69,70,71,72,74,75,76,77,80,81,82,83,85,86,87,88,91,92,93,94,96,97 %N A231003 Number of years after which it is not possible to have a date falling on the same day of the week, in the Julian calendar. %C A231003 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 A231003 Assuming this fact, this sequence is periodic with a period of 28. %C A231003 This is the complement of A231000. %H A231003 Time And Date, <a href="http://www.timeanddate.com/calendar/repeating.html">Repeating Calendar</a> %H A231003 Time And Date, <a href="http://www.timeanddate.com/calendar/julian-calendar.html">Julian Calendar</a> %H A231003 <a href="/index/Rec#order_22">Index entries for linear recurrences with constant coefficients</a>, signature (1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,-1). %F A231003 From _Chai Wah Wu_, Jun 04 2024: (Start) %F A231003 a(n) = a(n-1) + a(n-21) - a(n-22) for n > 22. %F A231003 G.f.: x*(x^21 + x^20 + x^19 + x^18 + 3*x^17 + x^16 + x^15 + x^14 + 2*x^13 + x^12 + x^11 + x^10 + x^9 + 2*x^8 + x^7 + x^6 + x^5 + 3*x^4 + x^3 + x^2 + x + 1)/(x^22 - x^21 - x + 1). (End) %o A231003 (PARI) for(i=0,420,j=0;for(y=0,420,if(((5*(y\4)+(y%4))%7)==((5*((y+i)\4)+((y+i)%4))%7),j=1));if(j==0,print1(i", "))) %Y A231003 Cf. A230995-A231014. %Y A231003 Cf. A230998 (Gregorian calendar). %K A231003 nonn,easy %O A231003 1,2 %A A231003 _Aswini Vaidyanathan_, Nov 02 2013