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%I #18 Apr 21 2019 02:18:24
%S 1,-4,6,-4,-4,16,-24,16,16,-64,96,-64,-64,256,-384,256,256,-1024,1536,
%T -1024,-1024,4096,-6144,4096,4096,-16384,24576,-16384,-16384,65536,
%U -98304,65536,65536,-262144,393216,-262144,-262144,1048576,-1572864,1048576,1048576,-4194304,6291456
%N a(n) = -2*a(n-1) - 2*a(n-2), with a(0)=1 and a(1)=-4.
%H <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (-2,-2).
%F For n >= 4, a(n) = -4*a(n-4).
%F a(n) = (-1)^n*A137444(n) = A108520(n) - 2*A108520(n-1).
%F G.f.: (1-2*x)/(1 + 2*x + 2*x^2).
%F a(n) = (1/2 + 3*i/2)*(-1 + i)^n + (1/2 - 3*i/2)*(-1 - i)^n, n >= 0, where i=sqrt(-1). - _Taras Goy_, Apr 20 2019
%t LinearRecurrence[{-2,-2},{1,-4},50] (* _Harvey P. Dale_, Mar 26 2013 *)
%Y Cf. A108520, A137444.
%K sign,easy
%O 0,2
%A _Paul Curtz_, Apr 17 2008
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