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%I #7 Apr 16 2016 13:16:05
%S 1,3,7,20,50,138,356,964,2524,6768,17848,47624,126032,335472,889328,
%T 2364352,6273184,16667808,44242240,117516608,311995328,828603648,
%U 2200088960,5842620544,15513975040,41197898496,109395973888,290499691520,771395887616
%N Expansion of (1+x-3*x^2) / ( 1-2*x-4*x^2+6*x^3 ).
%C Sum of all second elements at level n of the TRIP-Stern sequence corresponding to the permutation triple (e,13,23)
%H 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 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (2,4,-6).
%F a(n) >= 2^n.
%o (PARI) x='x+O('x^99); Vec((1+x-3*x^2)/(1-2*x-4*x^2+6*x^3)) \\ _Altug Alkan_, Apr 16 2016
%Y Cf. A271486 (maximum at level n).
%K nonn,easy
%O 0,2
%A _R. J. Mathar_, Apr 16 2016
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