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 A078049 #27 Jan 30 2021 20:57:51
%S A078049 1,-2,0,5,-7,-3,22,-23,-24,92,-67,-141,367,-152,-723,1394,-100,-3411,
%T A078049 5005,1717,-15138,16709,15284,-63840,49981,92983,-256785,120800,
%U A078049 485753,-984138,133432,2320597,-3571599,-936163,10399958,-12099231,-9636848,44235268,-37060803,-61046581,179403455
%N A078049 Expansion of (1-x)/(1+x+2*x^2-x^3).
%H A078049 Michael De Vlieger, <a href="/A078049/b078049.txt">Table of n, a(n) for n = 0..4925</a>
%H A078049 Yüksel Soykan, <a href="https://arxiv.org/abs/1910.03490">Summing Formulas For Generalized Tribonacci Numbers</a>, arXiv:1910.03490 [math.GM], 2019.
%H A078049 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (-1,-2,1).
%F A078049 G.f.: (-1 + x)/(-1 - x - 2*x^2 + x^3). - _Michael De Vlieger_, Jan 09 2020
%t A078049 LinearRecurrence[{-1,-2,1},{1,-2,0},50] (* _Harvey P. Dale_, Oct 27 2015 *)
%o A078049 (PARI) Vec((1-x)/(1+x+2*x^2-x^3)+O(x^99)) \\ _Charles R Greathouse IV_, Sep 27 2012
%Y A078049 First differences of A077978.
%K A078049 sign,easy
%O A078049 0,2
%A A078049 _N. J. A. Sloane_, Nov 17 2002
%E A078049 Deleted certain dangerous or potentially dangerous links. - _N. J. A. Sloane_, Jan 30 2021