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 A271898 #10 Apr 20 2016 18:09:07
%S A271898 1,4,12,32,84,224,604,1632,4404,11872,31996,86240,232468,626656,
%T A271898 1689244,4553568,12274676,33087840,89192252,240428512,648104148,
%U A271898 1747043040,4709365468,12694663264,34219997876,92244137056,248655211900,670280153824,1806821104020,4870504494560,13129033073436
%N A271898 Expansion of ( 1+x^2 ) / ( 1-4*x+5*x^2-4*x^3 ).
%C A271898 Sum of all third elements at level n of the TRIP-Stern sequence corresponding to the permutation triple (e,e,e)
%H A271898 Harvey P. Dale, <a href="/A271898/b271898.txt">Table of n, a(n) for n = 0..1000</a>
%H A271898 Ilya Amburg, Krishna Dasaratha, Laure Flapan, Thomas Garrity, Chansoo Lee, Cornelia Mihaila, Nicholas Neumann-Chun, Sarah Peluse, Matthew Stoffregen, <a href="http://arxiv.org/abs/1509.05239">Stern Sequences for a Family of Multidimensional Continued Fractions: TRIP-Stern Sequences</a>, arXiv:1509.05239 [math.CO], 2015, Section 7.2.1
%H A271898 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (4,-5,4).
%t A271898 CoefficientList[Series[(1+x^2)/(1-4*x+5*x^2-4*x^3),{x,0,40}],x] (* or *) LinearRecurrence[{4,-5,4},{1,4,12},40] (* _Harvey P. Dale_, Apr 20 2016 *)
%o A271898 (PARI) x='x+O('x^99); Vec((1+x^2)/(1-4*x+5*x^2-4*x^3)) \\ _Altug Alkan_, Apr 16 2016
%Y A271898 Cf. A000930 (maximum at level n).
%K A271898 nonn,easy
%O A271898 0,2
%A A271898 _R. J. Mathar_, Apr 16 2016