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 A077931 #13 Jun 09 2018 07:56:03
%S A077931 1,-1,2,-4,9,-17,34,-68,137,-273,546,-1092,2185,-4369,8738,-17476,
%T A077931 34953,-69905,139810,-279620,559241,-1118481,2236962,-4473924,8947849,
%U A077931 -17895697,35791394,-71582788,143165577,-286331153,572662306,-1145324612,2290649225,-4581298449,9162596898
%N A077931 Expansion of 1/((1-x)*(1+2*x+x^2+2*x^3)).
%H A077931 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (-1,1,-1,2).
%t A077931 CoefficientList[Series[1/((1 - x) * (1 + 2 x + x^2 + 2 x^3)), {x, 0, 50}], x] (* _Vladimir Joseph Stephan Orlovsky_, Jun 20 2011 *)
%o A077931 (PARI) Vec(1/((1-x)*(1+2*x+x^2+2*x^3))+O(x^99)) \\ _Charles R Greathouse IV_, Sep 27 2012
%K A077931 sign,easy
%O A077931 0,3
%A A077931 _N. J. A. Sloane_, Nov 17 2002