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 A077906 #10 Oct 13 2023 16:17:31
%S A077906 1,0,1,-2,3,-4,9,-14,23,-40,69,-114,195,-332,561,-950,1615,-2736,4637,
%T A077906 -7866,13339,-22612,38345,-65022,110247,-186936,316981,-537474,911347,
%U A077906 -1545308,2620257,-4442950,7533567,-12774080,21659981,-36727114,62275275,-105595236,179049465,-303600014
%N A077906 Expansion of (1-x)^(-1)/(1+x+2*x^3).
%H A077906 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0,1,-2,2).
%t A077906 CoefficientList[Series[(1-x)^(-1)/(1+x+2x^3),{x,0,50}],x] (* or *) LinearRecurrence[{0,1,-2,2},{1,0,1,-2},50] (* _Harvey P. Dale_, Oct 13 2023 *)
%o A077906 (PARI) Vec((1-x)^(-1)/(1+x+2*x^3)+O(x^99)) \\ _Charles R Greathouse IV_, Sep 27 2012
%Y A077906 Cf. A003229.
%K A077906 sign,easy
%O A077906 0,4
%A A077906 _N. J. A. Sloane_, Nov 17 2002