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 A288834 #34 Jan 18 2021 02:37:59
%S A288834 2,9,36,135,486,1701,5832,19683,65610,216513,708588,2302911,7440174,
%T A288834 23914845,76527504,243931419,774840978,2453663097,7748409780,
%U A288834 24407490807,76709256822,240588123669,753145430616,2353579470675,7343167948506,22876792454961
%N A288834 a(n) = (n+1) * 3^(n-1).
%H A288834 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (6,-9).
%F A288834 O.g.f.: z*(2-3*z)/(1-3*z)^2.
%F A288834 a(n) = -A287768(n+1,2).
%F A288834 a(n) = (n+1)*A000244(n-1). - _Felix Fröhlich_, Jun 19 2017
%F A288834 a(n) = A027471(n)/3 for n >= 3. - _Art Baker_, Apr 12 2019
%F A288834 From _Amiram Eldar_, Jan 18 2021: (Start)
%F A288834 Sum_{n>=1} 1/a(n) = 9*log(3/2) - 3.
%F A288834 Sum_{n>=1} (-1)^(n+1)/a(n) = 3 - 9*log(4/3). (End)
%t A288834 Table[(n + 1)*3^(n - 1), {n, 27}] (* _Michael De Vlieger_, Jun 23 2017 *)
%t A288834 LinearRecurrence[{6,-9},{2,9},40] (* _Harvey P. Dale_, Dec 16 2018 *)
%o A288834 (PARI) a(n) = (n+1)*3^(n-1) \\ _Felix Fröhlich_, Jun 19 2017
%o A288834 (PARI) Vec((z*(2-3*z)/(1-3*z)^2) + O(z^30)) \\ _Felix Fröhlich_, Jun 19 2017
%Y A288834 Cf. A000244, A027471, A287768.
%K A288834 nonn
%O A288834 1,1
%A A288834 _Gregory Gerard Wojnar_, Jun 17 2017