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A052957
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Expansion of 2*(1-x-x^2)/((1-2x)(1-2x^2)).
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1
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2, 2, 6, 8, 20, 32, 72, 128, 272, 512, 1056, 2048, 4160, 8192, 16512, 32768, 65792, 131072, 262656, 524288, 1049600, 2097152, 4196352, 8388608, 16781312, 33554432, 67117056, 134217728, 268451840, 536870912, 1073774592, 2147483648
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,1
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LINKS
| INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 1028
Index to sequences with linear recurrences with constant coefficients, signature (2,2,-4).
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FORMULA
| G.f.: -2*(-1+x+x^2)/(-1+2*x^2)/(-1+2*x)
Recurrence: {a(1)=2, a(2)=6, a(0)=2, 4*a(n)-2*a(n+1)-2*a(n+2)+a(n+3)=0}
2^n+Sum(1/2*_alpha^(-n), _alpha=RootOf(-1+2*_Z^2))
a(n) = 2*A051437(n+1). - R. J. Mathar, Nov 27 2011
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MAPLE
| spec := [S, {S=Union(Sequence(Prod(Union(Z, Z), Z)), Sequence(Union(Z, Z)))}, unlabeled ]: seq(combstruct[count ](spec, size=n), n=0..20);
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CROSSREFS
| Sequence in context: A054153 A000673 A129383 * A197465 A157253 A074933
Adjacent sequences: A052954 A052955 A052956 * A052958 A052959 A052960
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KEYWORD
| easy,nonn
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AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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EXTENSIONS
| More terms from James A. Sellers (sellersj(AT)math.psu.edu), Jun 05 2000
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