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 A074611 #22 Jan 14 2024 02:30:40
%S A074611 2,9,41,189,881,4149,19721,94509,456161,2215269,10814201,53022429,
%T A074611 260917841,1287811989,6371951081,31591319949,156882857921,
%U A074611 780119322309,3883416742361,19348364235069,96466943268401,481235204714229
%N A074611 a(n) = 4^n + 5^n.
%H A074611 Vincenzo Librandi, <a href="/A074611/b074611.txt">Table of n, a(n) for n = 0..1000</a>
%H A074611 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (9,-20).
%F A074611 From _Mohammad K. Azarian_, Jan 11 2009: (Start)
%F A074611 G.f.: 1/(1-4*x) + 1/(1-5*x).
%F A074611 E.g.f.: exp(4*x) + exp(5*x). (End)
%F A074611 a(n) = 9*a(n-1) - 20*a(n-2), with n>1, a(0)=2, a(1)=9. - _Vincenzo Librandi_, Jul 21 2010
%t A074611 Table[4^n + 5^n, {n, 0, 25}]
%t A074611 CoefficientList[Series[1/(1 - 4 x) + 1/(1 - 5 x), {x, 0, 30}], x] (* _Vincenzo Librandi_, Feb 06 2013 *)
%o A074611 (Magma) [4^n + 5^n: n in [0..30]]; // _Vincenzo Librandi_, Feb 06 2013
%o A074611 (SageMath) [4^+5^n for n in range(31)] # _G. C. Greubel_, Jan 13 2024
%Y A074611 Cf. A000051, A007689, A034472, A034474, A034491, A052539, A062394.
%Y A074611 Cf. A062395, A062396, A063376, A063481, A074600 - A074624.
%K A074611 easy,nonn
%O A074611 0,1
%A A074611 _Robert G. Wilson v_, Aug 25 2002