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 A099138 #9 Feb 18 2023 21:16:19
%S A099138 0,1,6,108,1080,14256,163296,2006208,23794560,287214336,3436494336,
%T A099138 41298398208,495217981440,5944792559616,71324450021376,
%U A099138 855971764420608,10271190988062720,123257112966660096,1479068428940476416
%N A099138 a(n) = 6^(n-1)*J(n), where J(n) = A001045(n).
%C A099138 In general k^(n-1)*J(n), where J(n) = A001045(n), is given by ((2*k)^n - (-k)^n)/(3*k) with g.f. x/((1+k*x)*(1-2*k*x)).
%H A099138 G. C. Greubel, <a href="/A099138/b099138.txt">Table of n, a(n) for n = 0..925</a>
%H A099138 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (6,72).
%F A099138 G.f.: x/((1+6*x)*(1-12*x)).
%F A099138 a(n) = 6^(n-1)*Sum_{k=0..floor((n-1)/2)} binomial(n-k-1, k) * 2^k.
%F A099138 a(n) = (12^n - (-6)^n)/18.
%F A099138 a(n) = 6^(n-1)*A001045(n).
%F A099138 E.g.f.: (1/18)*(exp(12*x) - exp(-6*x)). - _G. C. Greubel_, Feb 18 2023
%t A099138 LinearRecurrence[{6,72}, {0,1}, 40] (* _G. C. Greubel_, Feb 18 2023 *)
%o A099138 (Magma) [(12^n - (-6)^n)/18: n in [0..40]]; // _G. C. Greubel_, Feb 18 2023
%o A099138 (SageMath) [(12^n - (-6)^n)/18 for n in range(41)] # _G. C. Greubel_, Feb 18 2023
%Y A099138 Cf. A001045, A003683, A080424, A091903, A091904.
%K A099138 easy,nonn
%O A099138 0,3
%A A099138 _Paul Barry_, Sep 29 2004