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 A224949 #15 Jul 21 2024 20:13:20
%S A224949 1604,1632,1660,1688,1728,1756,1784,1824,1852,1880,1920,1948,1976,
%T A224949 2004,2032,2060,2088,2128,2156,2184,2224,2252,2280,2320,2348,2376,
%U A224949 2404,2432,2460,2488,2528,2556,2584,2624,2652,2680,2720,2748,2776
%N A224949 Leap years having 53 Thursdays and Fridays.
%C A224949 Gregorian calendar repeats after every 400 years because number of days in 400 years is 146097 which is a multiple of 7.
%C A224949 Non-century years are leap years if and only if they are multiples of 4 while century years are leap years if and only if they are multiples of 400.
%C A224949 13 occurrences in 400 years.
%C A224949 Months having Friday the 13th: February and August.
%C A224949 February 29th falls on Sunday.
%C A224949 366 day leap year: 52 Sundays, 52 Mondays, 52 Tuesdays, 52 Wednesdays, 53 Thursdays, 53 Fridays, 52 Saturdays.
%H A224949 Time and Date, <a href="http://www.timeanddate.com/calendar/gregorian-calendar.html">The Gregorian calendar</a>
%H A224949 Time and Date, <a href="http://www.timeanddate.com/calendar/?year=2004">2004</a>
%H A224949 Wikipedia, <a href="http://en.wikipedia.org/wiki/Gregorian_calendar">Gregorian calendar</a>
%H A224949 <a href="/index/Ca#calendar">Index entries for sequences related to calendars</a>
%H A224949 <a href="/index/Rec#order_14">Index entries for linear recurrences with constant coefficients</a>, signature (1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, -1).
%t A224949 Needs["Calendar`"]; Select[Range[1583, 2800], DayOfWeek[{#, 1, 1}, Calendar -> Gregorian] == Thursday && DaysBetween[{#, 1, 1}, {# + 1, 1, 1}, Calendar -> Gregorian] == 366 &, 50] (* _T. D. Noe_, Apr 22 2013 *)
%t A224949 Select[Range[1583,3000],LeapYearQ[{#}]&&DayName[{#,1,1}]==Thursday&] (* _Ray Chandler_, Jul 26 2023, v9 or later, after _Harvey P.Dale_ at A224945 *)
%Y A224949 Cf. A224945, A224946, A224947, A224948, A224950, A224951.
%K A224949 nonn
%O A224949 1,1
%A A224949 _Aswini Vaidyanathan_, Apr 21 2013