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 A199931 #23 Jan 05 2025 19:51:39
%S A199931 -1,2,4,-15,-2,79,-88,-294,815,488,-4769,3438,20080,-42527,-49666,
%T A199931 278943,-93220,-1308634,2103343,4067664,-15799793,-1126550,82089836,
%U A199931 -96324543,-299451394,864290495,454552096,-4979131422,3870112831,20615805880,-45400053553,-48829731594,292575692408
%N A199931 Trisection 1 of A199803.
%H A199931 Colin Barker, <a href="/A199931/b199931.txt">Table of n, a(n) for n = 0..1000</a>
%H A199931 Hirschhorn, Michael D., <a href="https://web.archive.org/web/2024*/https://www.fq.math.ca/43-4.html">Non-trivial intertwined second-order recurrence relations</a>, Fibonacci Quart. 43 (2005), no. 4, 316-325. See p. 324.
%H A199931 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (-1,-5,1,-1).
%F A199931 From _Colin Barker_, Dec 27 2017: (Start)
%F A199931 G.f.: -(1 - x - x^2) / (1 + x + 5*x^2 - x^3 + x^4).
%F A199931 a(n) = -a(n-1) - 5*a(n-2) + a(n-3) - a(n-4) for n>3.
%F A199931 (End)
%t A199931 CoefficientList[ Series[(-1 +x +x^2)/(1 +x +5x^2 -x^3 +x^4), {x, 0, 30}], x] (* or *)
%t A199931 LinearRecurrence[{-1, -5, 1, -1}, {-1, 2, 4, -15}, 30] (* _Robert G. Wilson v_, Dec 27 2017 *)
%o A199931 (PARI) Vec(-(1 - x - x^2) / (1 + x + 5*x^2 - x^3 + x^4) + O(x^40)) \\ _Colin Barker_, Dec 27 2017
%K A199931 sign,easy
%O A199931 0,2
%A A199931 _N. J. A. Sloane_, Nov 12 2011