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 A033171 #12 Jan 25 2020 02:20:32 %S A033171 365,730,1095,1461,1826,2191,2556,2922,3287,3652,4017,4383,4748,5113, %T A033171 5478,5844,6209,6574,6939,7305,7670,8035,8400,8766,9131,9496,9861, %U A033171 10227,10592,10957,11322,11688,12053,12418,12783,13149,13514,13879 %N A033171 Number of days in n years (n=4 is the first leap year). %F A033171 From _Chai Wah Wu_, Jan 25 2020: (Start) %F A033171 As the beginning year is not specified, the sequence is only well-defined if we ignore the rule where if a year is divisible by 100 but not by 400, it is not a leap year. Assuming that, we have the following formulas: %F A033171 a(n) = a(n-1) + a(n-4) - a(n-5) for n > 5. %F A033171 G.f.: x*(366*x^3 + 365*x^2 + 365*x + 365)/(x^5 - x^4 - x + 1). (End) %K A033171 easy,nonn %O A033171 1,1 %A A033171 _Jeff Burch_