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 A199299 #25 May 08 2023 09:34:54
%S A199299 1,18,180,1512,11664,85536,606528,4199040,28553472,191476224,
%T A199299 1269789696,8344332288,54419558400,352638738432,2272560758784,
%U A199299 14575734521856,93096626946048,592433080565760,3757718396731392,23765029860409344,149902496042582016,943288877536247808
%N A199299 a(n) = (2*n + 1)*6^n.
%H A199299 Vincenzo Librandi, <a href="/A199299/b199299.txt">Table of n, a(n) for n = 0..1000</a>
%H A199299 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (12,-36).
%F A199299 a(n) = 12*a(n-1) - 36*a(n-2).
%F A199299 G.f.: (1+6*x)/(1-6*x)^2.
%F A199299 a(n) = 6*a(n-1) + 2*6^n. - _Vincenzo Librandi_, Nov 05 2011
%F A199299 From _Amiram Eldar_, Dec 10 2022: (Start)
%F A199299 Sum_{n>=0} 1/a(n) = sqrt(6)*arccoth(sqrt(6)).
%F A199299 Sum_{n>=0} (-1)^n/a(n) = sqrt(6)*arccot(sqrt(6)). (End)
%F A199299 E.g.f.: exp(6*x)*(1 + 12*x). - _Stefano Spezia_, May 07 2023
%t A199299 a[n_] := (2*n + 1)*6^n; Array[a, 25, 0] (* _Amiram Eldar_, Dec 10 2022 *)
%o A199299 (Magma) [(2*n+1)*6^n: n in [0..30]]; // _Vincenzo Librandi_, Nov 05 2011
%o A199299 (PARI) a(n) = (2*n+1)*6^n \\ _Amiram Eldar_, Dec 10 2022
%Y A199299 Cf. A014480, A058962, A124647, A155988, A171220, A199300, A199301.
%K A199299 nonn,easy
%O A199299 0,2
%A A199299 _Philippe Deléham_, Nov 04 2011