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%I #21 Jan 14 2024 02:30:08
%S 2,12,90,756,6642,59292,532170,4785156,43053282,387440172,3486843450,
%T 31381236756,282430067922,2541867422652,22876797237930,
%U 205891146443556,1853020231898562,16677181828806732,150094635684419610
%N a(n) = 3^n + 9^n.
%H G. C. Greubel, <a href="/A074610/b074610.txt">Table of n, a(n) for n = 0..1000</a>
%H <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (12,-27).
%F From _Mohammad K. Azarian_, Jan 11 2009: (Start)
%F G.f.: 1/(1-3*x) + 1/(1-9*x).
%F E.g.f.: exp(3*x) + exp(9*x). (End)
%F a(n) = 12*a(n-1) - 27*a(n-2) with a(0)=2, a(1)=12. - _Vincenzo Librandi_, Jul 21 2010
%F a(n) = 2*A025551(n). - _G. C. Greubel_, Jan 13 2024
%t Table[3^n + 9^n, {n, 0, 25}]
%t LinearRecurrence[{12,-27},{2,12},20] (* _Harvey P. Dale_, May 18 2023 *)
%o (Magma) [3^n+9^n: n in [0..30]]; // _G. C. Greubel_, Jan 13 2024
%o (SageMath) [3^n+9^n for n in range(31)] # _G. C. Greubel_, Jan 13 2024
%Y Cf. A000051, A007689, A025551, A034472, A034474, A034491, A052539.
%Y Cf. A062394, A062395, A062396, A063376, A063481, A074600..A074624.
%K easy,nonn
%O 0,1
%A _Robert G. Wilson v_, Aug 25 2002
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