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%I #20 Jun 29 2023 12:29:24
%S 3,6,18,54,162,486,1458,4374,13122,39366,118098,354294,1062882,
%T 3188646,9565938,28697814,86093442,258280326,774840978,2324522934,
%U 6973568802,20920706406,62762119218,188286357654,564859072962,1694577218886
%N a(1) = 3, a(n+1) = 2*(3^n).
%C Same as A025192 for n > 1. - _Georg Fischer_, Oct 21 2018
%H G. C. Greubel, <a href="/A110593/b110593.txt">Table of n, a(n) for n = 1..1000</a>
%H <a href="/index/Rec#order_01">Index entries for linear recurrences with constant coefficients</a>, signature (3).
%F a(n) = A008776(n-1) for n>1. - _R. J. Mathar_, Apr 24 2007
%F G.f.: 3*x + 6*x^2/(1-3*x). - _R. J. Mathar_, Nov 18 2007
%t Rest[CoefficientList[Series[3 x + 6 x^2/(1 - 3 x), {x, 0, 50}], x]] (* _G. C. Greubel_, Sep 01 2017 *)
%o (PARI) x='x+O('x^50); Vec(3*x + 6*x^2/(1-3*x)) \\ _G. C. Greubel_, Sep 01 2017
%Y Cf. A000244, A025192, A081604.
%K easy,less,nonn
%O 1,1
%A _Jonathan Vos Post_, Jul 29 2005
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