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 A098559 #26 Feb 02 2023 05:05:42
%S A098559 1,6,36,324,3888,58320,1049760,22044960,529079040,14285134080,
%T A098559 428554022400,14142282739200,509122178611200,19855764965836800,
%U A098559 833942128565145600,37527395785431552000,1801314997700714496000,91867064882736439296000,4960821503667767721984000
%N A098559 Expansion of e.g.f. (1+3*x)/(1-3*x).
%H A098559 Vincenzo Librandi, <a href="/A098559/b098559.txt">Table of n, a(n) for n = 0..200</a>
%F A098559 a(n) = 6 * A034001(n) for n >= 1.
%F A098559 a(n) = 2*3^n*n! - 0^n.
%F A098559 Sum_{n>=0} 1/a(n) = (exp(1/3)+1)/2. - _Amiram Eldar_, Feb 02 2023
%t A098559 Join[{1},Table[2*3^n n!,{n,20}]] (* _Harvey P. Dale_, Aug 08 2014 *)
%o A098559 (Magma) [2*3^n*Factorial(n)-0^n: n in [0..20]]; // _Vincenzo Librandi_, Aug 08 2014
%Y A098559 Cf. A098558, A032184.
%K A098559 easy,nonn
%O A098559 0,2
%A A098559 _Paul Barry_, Sep 14 2004