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a(0) = 0, a(1) = 1, a(2) = 3, a(3) = 2; thereafter a(n) = -4*a(n-4).
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%I #16 Jul 14 2022 20:29:10

%S 0,1,3,2,0,-4,-12,-8,0,16,48,32,0,-64,-192,-128,0,256,768,512,0,-1024,

%T -3072,-2048,0,4096,12288,8192,0,-16384,-49152,-32768,0,65536,196608,

%U 131072,0,-262144,-786432,-524288,0,1048576,3145728,2097152,0,-4194304,-12582912,-8388608,0,16777216,50331648

%N a(0) = 0, a(1) = 1, a(2) = 3, a(3) = 2; thereafter a(n) = -4*a(n-4).

%C First and third differences have only 2^n's.

%H G. C. Greubel, <a href="/A138377/b138377.txt">Table of n, a(n) for n = 0..1000</a>

%H <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0, 0, 0, -4).

%F From _R. J. Mathar_, May 09 2008: (Start)

%F O.g.f.: x*(1+x)*(2*x+1)/((1-2*x+2*x^2)*(1+2*x+2*x^2)).

%F a(n) = (5*A009545(n) - A108520(n))/4. (End)

%t LinearRecurrence[{0,0,0,-4},{0,1,3,2},60] (* _Harvey P. Dale_, Mar 19 2012 *)

%o (PARI) x='x+O('x^25); Vec(x*(1+x)*(2*x+1)/((1-2*x+2*x^2)*(1+2*x+2*x^2))) \\ _G. C. Greubel_, Feb 20 2017

%Y Cf. A138380, A138382.

%K sign,easy

%O 0,3

%A _Paul Curtz_, May 08 2008