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 A098577 #12 Sep 08 2022 08:45:15
%S A098577 1,1,1,1,1,3,7,13,21,31,47,77,133,231,391,645,1053,1727,2863,4781,
%T A098577 7989,13303,22071,36565,60621,100655,167295,278077,461989,767143,
%U A098577 1273607,2114661,3511869,5833055,9688527,16091213,26723221,44378967,73700823
%N A098577 a(n) = Sum_{k=0..floor(n/5)} C(n-3*k,2*k) * 2^k.
%H A098577 G. C. Greubel, <a href="/A098577/b098577.txt">Table of n, a(n) for n = 0..1000</a>
%H A098577 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (2,-1,0,0,2).
%F A098577 G.f.: (1-x)/((1-x)^2-2*x^5).
%F A098577 a(n) = a(n-1) - a(n-2) + 2*a(n-5).
%t A098577 LinearRecurrence[{2,-1,0,0,2},{1,1,1,1,1},40] (* _Harvey P. Dale_, Feb 11 2015 *)
%t A098577 CoefficientList[Series[(1-x)/((1-x)^2-2*x^5), {x,0,50}], x] (* _G. C. Greubel_, Feb 03 2018 *)
%o A098577 (PARI) x='x+O('x^30); Vec((1-x)/((1-x)^2-2*x^5)) \\ _G. C. Greubel_, Feb 03 2018
%o A098577 (Magma) I:=[1,1,1,1,1,]; [n le 5 select I[n] else 2*Self(n-1) -Self(n-2) + 2*Self(n-5): n in [1..30]]; // _G. C. Greubel_, Feb 03 2018
%Y A098577 Cf. A098575, A005253.
%K A098577 easy,nonn
%O A098577 0,6
%A A098577 _Paul Barry_, Sep 16 2004