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A138340
Expansion of (1-8x)/(1-4x+16x^2).
2
1, -4, -32, -64, 256, 2048, 4096, -16384, -131072, -262144, 1048576, 8388608, 16777216, -67108864, -536870912, -1073741824, 4294967296, 34359738368, 68719476736, -274877906944, -2199023255552, -4398046511104, 17592186044416
OFFSET
0,2
COMMENTS
abs(a(n)) = 2^A047267(n).
FORMULA
a(n) = 2*4^n(cos(Pi*(n+1)/3) - sqrt(3)*sin(Pi*(n+1))/3).
a(n) = 4^n*Sum_{k=0..n} A121314(n,k)*(-1)^k*3^(n-k). - Philippe Deléham, Nov 01 2008
a(n) = A128018(n)*2^n. - Philippe Deléham, Nov 14 2008
a(n) = 4*a(n-1) - 16*a(n-2); a(0)=1, a(1)=-4. - Harvey P. Dale, Sep 30 2014
MATHEMATICA
CoefficientList[Series[(1-8x)/(1-4x+16x^2), {x, 0, 30}], x] (* or *) LinearRecurrence[{4, -16}, {1, -4}, 30] (* Harvey P. Dale, Sep 30 2014 *)
CROSSREFS
Sequence in context: A114076 A078092 A076137 * A113250 A329910 A012036
KEYWORD
easy,sign
AUTHOR
Paul Barry, Mar 15 2008
STATUS
approved