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 A098581 #14 Sep 08 2022 08:45:15
%S A098581 1,3,7,7,15,39,95,151,271,583,1343,2551,4719,9383,20127,40535,78287,
%T A098581 153351,314367,638647,1264943,2491751,5006687,10115863,20235407,
%U A098581 40169415,80222911,161149815,323033071,644388391,1286171679,2575370199
%N A098581 Expansion of (1+2*x+4*x^2)/(1-x-8*x^4).
%H A098581 Harvey P. Dale, <a href="/A098581/b098581.txt">Table of n, a(n) for n = 0..1000</a>
%H A098581 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (1,0,0,8).
%F A098581 a(n) = a(n-1) + 8*a(n-4).
%F A098581 a(n) = Sum_{k=0..n} binomial(n-k, floor(k/3)) * 2^k.
%t A098581 CoefficientList[Series[(1+2x+4x^2)/(1-x-8x^4),{x,0,40}],x] (* or *) LinearRecurrence[{1,0,0,8},{1,3,7,7},40] (* _Harvey P. Dale_, Feb 04 2015 *)
%o A098581 (PARI) x='x+O('x^30); Vec((1+2*x+4*x^2)/(1-x-8*x^4)) \\ _G. C. Greubel_, Feb 03 2018
%o A098581 (Magma) I:=[1,3,7,7]; [n le 4 select I[n] else Self(n-1) + 8*Self(n-4): n in [1..30]]; // _G. C. Greubel_, Feb 03 2018
%Y A098581 Cf. A078467, A097334.
%K A098581 easy,nonn
%O A098581 0,2
%A A098581 _Paul Barry_, Sep 16 2004