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 A219205 #26 Feb 14 2024 10:46:40
%S A219205 0,2,24,234,2160,19602,176904,1593594,14346720,129133602,1162241784,
%T A219205 10460294154,94143001680,847288078002,7625595890664,68630372581914,
%U A219205 617673381935040,5559060523508802,50031544969859544,450283905503576874
%N A219205 a(n) = 3^(n-1)*(3^n - 1), n >= 0.
%C A219205 Last digit has period 4: 0, 2, 4, 4.
%H A219205 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (12,-27).
%F A219205 a(n) = 2 * A016142(n-1).
%F A219205 a(n) = 12*a(n-1)-27*a(n-2). G.f.: 2*x/((3*x-1)*(9*x-1)). [_Colin Barker_, Nov 23 2012]
%t A219205 LinearRecurrence[{12, -27}, {0, 2}, 20] (* _Hugo Pfoertner_, Feb 14 2024 *)
%o A219205 (JavaScript)
%o A219205 for (j=0;j<20;j++) document.write((Math.pow(3,j)-1)*Math.pow(3,j-1)+", ");
%o A219205 (Maxima) A219205(n):=3^(n-1)*(3^n - 1)$ makelist(A219205(n),n,0,30); /* _Martin Ettl_, Nov 15 2012 */
%Y A219205 Cf. A006516, A016142.
%K A219205 nonn,easy
%O A219205 0,2
%A A219205 _Jon Perry_, Nov 14 2012
%E A219205 a(19) corrected by _Colin Barker_, Nov 23 2012