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 A074557 #12 Sep 08 2022 08:45:07
%S A074557 3,18,126,972,7938,67068,578826,5065092,44732898,397517868,3547309626,
%T A074557 31744033812,284606850258,2554928116668,22955161402026,
%U A074557 206361331428132,1855841341806018,16694108488251468,150196195641088026
%N A074557 3^n + 6^n + 9^n.
%H A074557 Vincenzo Librandi, <a href="/A074557/b074557.txt">Table of n, a(n) for n = 0..1000</a>
%H A074557 <a href="/index/Rec">Index entries for linear recurrences with constant coefficients</a>, signature (18,-99,162).
%F A074557 G.f.: 1/(1-3*x)+1/(1-6*x)+1/(1-9*x). E.g.f.: exp(3*x)+exp(6*x)+exp(9*x). [From _Mohammad K. Azarian_, Dec 30 2008]
%t A074557 Table[3^n + 6^n + 9^n, {n, 0, 20}]
%o A074557 (Magma) [3^n + 6^n + 9^n: n in [0..20]]; // Vincenzo Librandi, Aug 24 2011
%Y A074557 Cf. A001550, A001576, A034513, A001579, A074501 - A074580.
%K A074557 easy,nonn
%O A074557 0,1
%A A074557 _Robert G. Wilson v_, Aug 23 2002