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a(n) = 4*3^n - 3*2^n.
9

%I #39 May 18 2024 14:54:00

%S 1,6,24,84,276,876,2724,8364,25476,77196,233124,702444,2113476,

%T 6352716,19082724,57297324,171990276,516167436,1548895524,4647473004,

%U 13943991876,41835121356,125511655524,376547549484,1129667814276,3389053774476,10167261986724,30501987286764

%N a(n) = 4*3^n - 3*2^n.

%C Second binomial transform of A123932 = [1,4,4,4,4,4,4,4,...].

%H Vincenzo Librandi, <a href="/A166060/b166060.txt">Table of n, a(n) for n = 0..1000</a>

%H John Elias, <a href="/A166060/a166060.png">Illustration of initial terms: Sierpinski-tetra-triangles</a>

%H <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (5,-6).

%F a(n) = 5*a(n-1) - 6*a(n-2) for n > 1; a(0)= 1, a(1)= 6.

%F G.f.: (1+x)/(1-5x+6x^2).

%F a(n) = A217764(n,6). - _Ross La Haye_, Mar 27 2013

%F a(n) = Sum_{k = 1..2^n} A082560(n+1,k). - _Reinhard Zumkeller_, May 14 2015

%F E.g.f.: exp(2*x)*(4*exp(x) - 3). - _Stefano Spezia_, May 18 2024

%t CoefficientList[Series[(1+x)/((1-2x)*(1-3x)), {x, 0, 30}], x] (* _Vincenzo Librandi_, Dec 05 2012 *)

%o (PARI) a(n)=4*3^n-3<<n \\ _Charles R Greathouse IV_, Jan 12 2012

%o (Magma) [4*3^n-3*2^n: n in [0..30]]; // _Vincenzo Librandi_, Dec 05 2012

%o (Haskell)

%o a166060 n = a166060_list !! n

%o a166060_list = map fst $ iterate (\(u, v) -> (3 * (u + v), 2 * v)) (1, 1)

%o -- _Reinhard Zumkeller_, Jun 09 2013

%Y Cf. A082560, A123932, A217764, A257956.

%K nonn,easy

%O 0,2

%A _Philippe Deléham_, Oct 05 2009

%E a(19) and a(22) corrected by _Charles R Greathouse IV_, Jan 12 2012