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 A077890 #5 Apr 07 2018 08:01:27
%S A077890 1,1,0,-2,-1,3,6,0,-11,-11,12,34,11,-57,-78,36,193,121,-264,-506,23,
%T A077890 1035,990,-1080,-3059,-899,5220,7018,-3421,-17457,-10614,24300,45529,
%U A077890 -3071,-94128,-87986,100271,276243,75702,-476784,-628187,325381,1581756,930994,-2232517,-4094505,370530
%N A077890 Expansion of (1-x)^(-1)/(1+x^2+2*x^3).
%H A077890 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (1,-1,-1,2).
%t A077890 CoefficientList[Series[(1-x)^(-1)/(1+x^2+2*x^3),{x,0,50}],x] (* or *) LinearRecurrence[{1,-1,-1,2},{1,1,0,-2},50] (* _Harvey P. Dale_, Apr 07 2018 *)
%K A077890 sign
%O A077890 0,4
%A A077890 _N. J. A. Sloane_, Nov 17 2002