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 A199853 #29 May 31 2021 12:50:46
%S A199853 1,-1,-1,-3,-6,-14,-31,-70,-157,-353,-793,-1782,-4004,-8997,-20216,
%T A199853 -45425,-102069,-229347,-515338,-1157954,-2601899,-5846414,-13136773,
%U A199853 -29518061,-66326481,-149034250,-334876920,-752461609,-1690765888,-3799116465,-8536537209
%N A199853 Expansion of (1-3*x+x^3)/(1-2*x-x^2+x^3).
%H A199853 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (2,1,-1).
%F A199853 a(n) = 2*a(n-1) + a(n-2) - a(n-3) with a(0)=1, a(1)=-1, a(2)=-1, a(3)=-3.
%F A199853 a(n+1) = - A077998(n). - _G. C. Greubel_, Aug 14 2015
%t A199853 RecurrenceTable[{a[1]==-1, a[2]== -1, a[3]== -3, a[n]== 2*a[n-1] + a[n-2] - a[n-3]}, a, {n,30}] (* _G. C. Greubel_, Aug 13 2015 *)
%t A199853 CoefficientList[Series[(1-3x+x^3)/(1-2x-x^2+x^3),{x,0,30}],x] (* or *) LinearRecurrence[{2,1,-1},{1,-1,-1,-3},40] (* _Harvey P. Dale_, May 31 2021 *)
%o A199853 (PARI) Vec((1-3*x+x^3)/(1-2*x-x^2+x^3) + O(x^40)) \\ _Michel Marcus_, Aug 13 2015
%Y A199853 Cf. A006356, A077998, A180262.
%K A199853 sign,easy
%O A199853 0,4
%A A199853 _Philippe Deléham_, Nov 11 2011