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 A108369 #20 Aug 05 2024 08:41:45
%S A108369 0,1,-3,6,-8,3,21,-80,180,-279,217,366,-2028,5203,-9159,9840,3160,
%T A108369 -48159,144837,-286874,377952,-128397,-1035539,3869760,-8631060,
%U A108369 13248361,-9982143,-18429714,98483932,-250144797,436552881,-460740320,-177582480,2351521281
%N A108369 Coefficients of x/(1+3*x+3*x^2-x^3).
%D A108369 L. E. Dickson, History of the Theory of Numbers. Carnegie Institute Public. 256, Washington, DC, Vol. 1, 1919; Vol. 2, 1920; Vol. 3, 1923, see vol. 2, p. 562.
%H A108369 Harvey P. Dale, <a href="/A108369/b108369.txt">Table of n, a(n) for n = 0..1000</a>
%H A108369 Vincent Thill, <a href="http://vincent-thill.fr/2021/04/identite-du-mois-davril-2021/">Radicaux et Ramanujan</a>, April 2021, see c(n).
%H A108369 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (-3,-3,1).
%F A108369 x=a(n), z=a(-n-2), y=a(n)+a(n+1), t=a(-1-n)+a(-n-2) is a solution to 2*(x^3+z^3) = y^3+t^3.
%F A108369 G.f.: x/(1+3*x+3*x^2-x^3).
%F A108369 a(n) = -3*a(n-1) - 3*a(n-2) + a(n-3).
%F A108369 a(-1-n) = A108368(n).
%F A108369 a(n+1) = (-1)^n * Sum_{k=0..floor(n/3)} (-2)^k * binomial(n+2,3*k+2). - _Seiichi Manyama_, Aug 05 2024
%t A108369 CoefficientList[Series[x/(1+3x+3x^2-x^3),{x,0,40}],x] (* or *) LinearRecurrence[{-3,-3,1},{0,1,-3},40] (* _Harvey P. Dale_, Jul 30 2024 *)
%o A108369 (PARI) {a(n)=if(n>=0, polcoeff(x/(1+3*x+3*x^2-x^3)+x*O(x^n),n), n=-1-n; polcoeff(x/(1-3*x-3*x^2-x^3)+x*O(x^n),n))}
%Y A108369 Cf. A000748, A108368.
%K A108369 sign
%O A108369 0,3
%A A108369 _Michael Somos_, Jun 01 2005