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 A129009 #26 Dec 28 2024 19:33:30
%S A129009 18,972,26244,524880,8857350,133923132,1874923848,24794911296,
%T A129009 313810596090,3835462841100,45565298552268,528708092292432,
%U A129009 6014054549826414,67257769817585340,741208075540736400
%N A129009 a(n) = (n^3 + n^2)*9^n.
%H A129009 Vincenzo Librandi, <a href="/A129009/b129009.txt">Table of n, a(n) for n = 1..1000</a>
%H A129009 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (36,-486,2916,-6561).
%F A129009 G.f.: 18*x*(1+18*x)/(1-9*x)^4. - _R. J. Mathar_, Dec 19 2008
%F A129009 a(n) = 36*a(n-1)-486*a(n-2)+2916*a(n-3)-6561*a(n-4). - _Vincenzo Librandi_, Feb 12 2013
%t A129009 LinearRecurrence[{36, -486, 2916, -6561}, {18, 972, 26244, 524880}, 30] (* _Vincenzo Librandi_, Feb 12 2013 *)
%o A129009 (Magma) [(n^3+n^2)*9^n: n in [1..25]]; // _Vincenzo Librandi_, Feb 12 2013
%o A129009 (Magma) I:=[18,972,26244,524880]; [n le 4 select I[n] else 36*Self(n-1)-486*Self(n-2)+2916*Self(n-3)-6561*Self(n-4): n in [1..25]]; // _Vincenzo Librandi_, Feb 12 2013
%Y A129009 Cf. A128796, A036289.
%K A129009 nonn,easy
%O A129009 1,1
%A A129009 _Mohammad K. Azarian_, May 01 2007