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 A255117 #21 Oct 12 2022 08:40:46
%S A255117 1,4,17,72,304,1284,5424,22912,96784,408832,1726976,7295040,30815488,
%T A255117 130169856,549859584,2322700288,9811480576,41445360640,175072243712,
%U A255117 739534897152,3123921031168,13195973099520,55742031986688,235463812071424,994639140683776
%N A255117 Number of n-length words on {0,1,2,3,4} in which 0 appears only in runs of length 2.
%H A255117 Colin Barker, <a href="/A255117/b255117.txt">Table of n, a(n) for n = 0..1000</a>
%H A255117 D. Birmajer, J. B. Gil, and M. D. Weiner, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL19/Gil/gil6.html">On the Enumeration of Restricted Words over a Finite Alphabet</a>, J. Int. Seq. 19 (2016) # 16.1.3, example 10.
%H A255117 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (4,0,4).
%F A255117 a(n+3) = 4*a(n+2) + 4*a(n) with n>1, a(0) = 1, a(1) = 4, a(2) = 17.
%F A255117 G.f.: -(x^2+1) / (4*x^3+4*x-1). - _Colin Barker_, Feb 15 2015
%F A255117 a(n) = A089979(n) + A089979(n-2). - _R. J. Mathar_, Aug 04 2019
%t A255117 RecurrenceTable[{a[0] == 1, a[1] == 4, a[2]== 17, a[n] == 4 a[n - 1] + 4 a[n - 3]}, a[n], {n, 0, 25}]
%o A255117 (PARI) Vec(-(x^2+1)/(4*x^3+4*x-1) + O(x^100)) \\ _Colin Barker_, Feb 15 2015
%Y A255117 Cf. A000930, A239333, A239340, A254657, A254600, A254664.
%K A255117 nonn,easy
%O A255117 0,2
%A A255117 _Milan Janjic_, Feb 14 2015