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 A199803 #26 Jan 05 2025 19:51:39
%S A199803 1,-1,2,-2,2,-1,-1,4,-8,12,-15,15,-10,-2,22,-49,79,-104,112,-88,17,
%T A199803 111,-294,510,-710,815,-721,316,488,-1708,3233,-4769,5806,-5634,3438,
%U A199803 1503,-9505,20080,-31520,40592,-42527,31519,-1934,-49666,121778,-204897,278943,-312396,264664,-93220,-233455,717295,-1308634,1885694,-2243578,2103343,-1152593,-873336
%N A199803 G.f.: 1/(1 + x - x^2 - x^3 + x^4).
%H A199803 Michael De Vlieger, <a href="/A199803/b199803.txt">Table of n, a(n) for n = 0..8475</a>
%H A199803 Michael D. Hirschhorn, <a href="https://web.archive.org/web/2024*/https://www.fq.math.ca/Papers1/43-4/paper43-4-5.pdf">Non-trivial intertwined second-order recurrence relations</a>, Fibonacci Quart. 43 (2005), no. 4, 316-325. See H_n.
%H A199803 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (-1,1,1,-1).
%F A199803 a(n) = -a(n-1) + a(n-2) + a(n-3) - a(n-4) for n > 3. - _Taras Goy_, Dec 24 2019
%t A199803 CoefficientList[Series[1/(1 + x - x^2 - x^3 + x^4), {x, 0, 57}], x] (* _Michael De Vlieger_, Dec 24 2019 *)
%t A199803 LinearRecurrence[{-1,1,1,-1},{1,-1,2,-2},60] (* _Harvey P. Dale_, Jan 17 2021 *)
%K A199803 sign,easy
%O A199803 0,3
%A A199803 _N. J. A. Sloane_, Nov 10 2011