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 A217628 #13 Sep 08 2022 08:46:04
%S A217628 1,9,243,19683,4782969,3486784401,7625597484987,50031545098999707,
%T A217628 984770902183611232881,58149737003040059690390169,
%U A217628 10301051460877537453973547267843,5474401089420219382077155933569751763,8727963568087712425891397479476727340041449
%N A217628 a(n) = 3^((n-1)*(n+2)/2).
%H A217628 Vincenzo Librandi, <a href="/A217628/b217628.txt">Table of n, a(n) for n = 1..60</a>
%F A217628 a(1) = 1, a(n) = a(n-1) * 3^n.
%F A217628 G.f.: G(0)/(2*x^3) - 1/(3*x)- 1/(3*x^2)- 1/(2*x^3), where G(k)= 1 + 3^(k-1)*x/(1 - 1/(1 + 1/G(k+1) )); (continued fraction). - _Sergei N. Gladkovskii_, Jul 28 2013
%t A217628 Table[3^((n-1) * (n+2)/2), {n, 1, 30}]
%o A217628 (Magma) I:=[1]; [n le 1 select I[n] else Self(n-1)*3^n: n in [1..20]]
%o A217628 (Maxima) A217628[n]:=3^((n-1)*(n+2)/2)$
%o A217628 makelist(A217628[n],n,1,30); /* _Martin Ettl_, Oct 29 2012 */
%Y A217628 Cf. A036442.
%K A217628 nonn
%O A217628 1,2
%A A217628 _Vincenzo Librandi_, Oct 24 2012