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 A074559 #16 Apr 11 2023 13:32:34
%S A074559 3,19,139,1099,9043,76099,649819,5608699,48818083,427793779,
%T A074559 3769318699,33358563499,296271355123,2638756433059,23555020310779,
%U A074559 210638707953499,1886253162468163,16909812342793939,151723049282330059
%N A074559 a(n) = 3^n + 7^n + 9^n.
%H A074559 Vincenzo Librandi, <a href="/A074559/b074559.txt">Table of n, a(n) for n = 0..1000</a>
%H A074559 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (19,-111,189).
%F A074559 From _Mohammad K. Azarian_, Dec 30 2008: (Start)
%F A074559 G.f.: 1/(1-3*x) + 1/(1-7*x) + 1/(1-9*x).
%F A074559 E.g.f.: exp(3*x) + exp(7*x) + exp(9*x). (End)
%F A074559 a(n) = 19*a(n-1) - 111*a(n-2) + 189*a(n-3). - _Wesley Ivan Hurt_, Apr 11 2023
%t A074559 Table[3^n + 7^n + 9^n, {n, 0, 20}]
%o A074559 (Magma) [3^n + 7^n + 9^n: n in [0..20]]; // _Vincenzo Librandi_, Aug 24 2011
%Y A074559 Cf. A001550, A001576, A034513, A001579, A074501 - A074580.
%K A074559 easy,nonn
%O A074559 0,1
%A A074559 _Robert G. Wilson v_, Aug 23 2002