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%I
%S 1,2,-2,-10,-2,38,46,-106,-290,134,1294,758,-4418,-7450,10222,40022,
%T -866,-160954,-157490,486326,1116286,-829018,-5294162,-1978090,
%U 19198558,27110918,-49683314,-158126986,40606270,673114214,510689134,-2181767722,-4224524258
%N a(n) = a(n-1) - 4*a(n-2), a(0)=1, a(1)=2.
%H <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (1,-4).
%F G.f.: (1+x)/(1-x+4*x^2).
%F a(n) = Sum_{k0..n} A133607(n,k)*2^k. - _Philippe Deléham_, Dec 29 2007
%F a(n) = (1/10)*i*sqrt(15)*(1/2 - (1/2)*i*sqrt(15))^n - (1/10)*i*sqrt(15)*(1/2 + (1/2)*i*sqrt(15))^n + (1/2)*(1/2 - (1/2)*i*sqrt(15))^n + (1/2)*(1/2 + (1/2)*i*sqrt(15))^n, with n >= 0 and i = sqrt(-1). - _Paolo P. Lava_, Nov 18 2008
%K easy,sign
%O 0,2
%A _Philippe Deléham_, Dec 28 2007
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