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 A121511 #16 Oct 19 2024 23:55:59
%S A121511 1,5,13,25,5,9,17,29,9,13,21,33,13,17,25,37,17,21,29,41,21,25,33,45,
%T A121511 25,29,37,49,29,33,41,53,33,37,45,57,37,41,49,61,41,45,53,65,45,49,57,
%U A121511 69,49,53,61,73,53,57,65,77,57,61,69,81,61,65,73,85,65,69,77
%N A121511 a(n) = a(n-1) + a(n-4) - a(n-5).
%C A121511 This sequence gives a linearly increasing triangle shaped form on plotting.
%H A121511 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (1,0,0,1,-1).
%F A121511 G.f.: -x*(-1-4*x-8*x^2-12*x^3+21*x^4)/((1+x)*(x^2+1)*(x-1)^2).
%F A121511 a(n) = n + 17/2 + 7*(-1)^n/2 + A057077(n+1)*A010720(n-1).
%t A121511 LinearRecurrence[{1,0,0,1,-1},{1,5,13,25,5},67] (* _James C. McMahon_, Oct 19 2024 *)
%o A121511 (PARI) Vec(-x*(-1-4*x-8*x^2-12*x^3+21*x^4)/((1+x)*(x^2+1)*(x-1)^2) + O(x^75)) \\ _Jinyuan Wang_, Jun 07 2020
%Y A121511 Cf. A001844.
%K A121511 nonn,easy
%O A121511 1,2
%A A121511 _Roger L. Bagula_, Sep 07 2006
%E A121511 Definition replaced by recurrence - The Assoc. Editors of the OEIS, Oct 14 2009
%E A121511 More terms from _Jinyuan Wang_, Jun 07 2020