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 A089683 #18 Jul 10 2025 04:14:24
%S A089683 81,6561,531441,43046721,3486784401,282429536481,22876792454961,
%T A089683 1853020188851841,150094635296999121,12157665459056928801,
%U A089683 984770902183611232881,79766443076872509863361,6461081889226673298932241,523347633027360537213511521,42391158275216203514294433201
%N A089683 a(n) = 3^(4*n).
%H A089683 Tanya Khovanova, <a href="http://www.tanyakhovanova.com/RecursiveSequences/RecursiveSequences.html">Recursive Sequences</a>.
%H A089683 <a href="/index/Rec#order_01">Index entries for linear recurrences with constant coefficients</a>, signature (81).
%F A089683 a(n) = 81^n.
%F A089683 G.f.: 81*x/(1-81*x). - _Philippe Deléham_, Nov 25 2008
%F A089683 From _Elmo R. Oliveira_, Jul 09 2025: (Start)
%F A089683 E.g.f.: exp(81*x) - 1.
%F A089683 a(n) = 81*a(n-1) for n > 1.
%F A089683 a(n) = A001019(n)^2 = A000244(A008586(n)). (End)
%t A089683 3^(4*Range[20]) (* or *) NestList[81#&,81,20] (* _Harvey P. Dale_, Apr 09 2012 *)
%o A089683 (PARI) my(x='x+O('x^16)); Vec(-81*x/(81*x-1)) \\ _Elmo R. Oliveira_, Jul 09 2025
%Y A089683 Cf. A000244, A001019, A008586, A009971.
%K A089683 nonn,easy
%O A089683 1,1
%A A089683 Douglas Winston (douglas.winston(AT)srupc.com), Jan 05 2004
%E A089683 More terms from _Harvey P. Dale_, Apr 09 2012