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 A098590 #30 Sep 08 2022 08:45:15
%S A098590 1,4,16,64,257,1032,4144,16640,66817,268300,1077344,4326016,17370881,
%T A098590 69751824,280084640,1124664576,4516029185,18133868564,72815558896,
%U A098590 292386900160,1174063629825,4714388387864,18930369110352,76013863341568
%N A098590 a(n) = 4^n for n = 0..3; for n > 3, a(n) = 4*a(n-1) + a(n-4).
%C A098590 a(n) equals the number of n-length words on {0,1,2,3,4} such that 0 appears only in a run which length is a multiple of 4. - _Milan Janjic_, Feb 17 2015
%H A098590 G. C. Greubel, <a href="/A098590/b098590.txt">Table of n, a(n) for n = 0..1000</a>
%H A098590 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (4,0,0,1).
%F A098590 G.f.: 1/(1-4*x-x^4).
%F A098590 a(n) = Sum_{k=0..floor(n/3)} binomial(n-3*k, k) * 4^(n-4*k).
%p A098590 K:=1/(1+4*z-z^4): Kser:=series(K, z=0, 30): seq(abs(coeff(Kser, z, n)), n= 0..23); # _Zerinvary Lajos_, Nov 08 2007
%t A098590 CoefficientList[Series[1/(1 - 4*x - x^4), {x, 0, 25}], x] (* _Zerinvary Lajos_, Mar 29 2007 *)
%t A098590 LinearRecurrence[{4,0,0,1},{0,1,4,16},30] (* _Harvey P. Dale_, Jul 22 2014 *)
%o A098590 (PARI) x='x+O('x^30); Vec(1/(1-4*x-x^4)) \\ _G. C. Greubel_, Feb 03 2018
%o A098590 (Magma) I:=[0,1,4,16]; [n le 4 select I[n] else 4*Self(n-1) +Self(n-4): n in [1..30]]; // _G. C. Greubel_, Feb 03 2018
%Y A098590 Cf. A052541.
%K A098590 easy,nonn
%O A098590 0,2
%A A098590 _Paul Barry_, Sep 16 2004