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A133631 a(n) = a(n-1) - 4*a(n-2), a(0)=1, a(1)=2. 1

%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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Last modified January 15 19:15 EST 2021. Contains 340189 sequences. (Running on oeis4.)