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 A018206 #23 Feb 02 2025 17:14:56
%S A018206 1,24,403,5850,78601,1007364,12509263,151886670,1813607701,
%T A018206 21378247704,249446413723,2886767617890,33183014997601,
%U A018206 379298878576044,4315144805143783,48895164279003510,552132521336304301
%N A018206 Expansion of 1/((1-3x)(1-10x)(1-11x)).
%H A018206 Vincenzo Librandi, <a href="/A018206/b018206.txt">Table of n, a(n) for n = 0..200</a>
%H A018206 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (24,-173,330).
%F A018206 a(0)=1, a(1)=24, a(2)=403; for n>2, a(n) = 24*a(n-1) -173*a(n-2) +330*a(n-3). - _Vincenzo Librandi_, Jul 02 2013
%F A018206 a(n) = 21*a(n-1) -110*a(n-2) +3^n. - _Vincenzo Librandi_, Jul 02 2013
%F A018206 a(n) = (7*11^(n+2) - 8*10^(n+2) + 3^(n+2))/56. [_Yahia Kahloune_, Jul 06 2013]
%t A018206 CoefficientList[Series[1 / ((1 - 3 x) (1 - 10 x) (1 - 11 x)), {x, 0, 20}], x] (* _Vincenzo Librandi_, Jul 02 2013 *)
%t A018206 LinearRecurrence[{24,-173,330},{1,24,403},20] (* _Harvey P. Dale_, Nov 25 2013 *)
%o A018206 (Magma) m:=20; R<x>:=PowerSeriesRing(Integers(), m); Coefficients(R!(1/((1-3*x)*(1-10*x)*(1-11*x)))); // _Vincenzo Librandi_, Jul 02 2013
%o A018206 (Magma) I:=[1, 24, 403]; [n le 3 select I[n] else 24*Self(n-1)-173*Self(n-2)+330*Self(n-3): n in [1..20]]; // _Vincenzo Librandi_, Jul 02 2013
%K A018206 nonn,easy
%O A018206 0,2
%A A018206 _N. J. A. Sloane_