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Search: id:A052994
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| A052994 |
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A simple regular expression. |
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+0
3
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| 0, 2, 2, 6, 12, 28, 62, 140, 314, 706, 1586, 3564, 8008, 17994, 40432, 90850, 204138, 458694, 1030676, 2315908, 5203798, 11692828, 26273546, 59036122, 132652962, 298068500, 669753840, 1504923218, 3381531776, 7598232930, 17073074418
(list; graph; listen)
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OFFSET
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0,2
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LINKS
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INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 1071
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FORMULA
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G.f.: -2*x*(-1+x)/(x^3-x^2-2*x+1)
Recurrence: {a(0)=0, a(1)=2, a(2)=2, a(n)-a(n+1)-2*a(n+2)+a(n+3)}
Sum(2/7*(-_alpha+_alpha^2+1)*_alpha^(-1-n), _alpha=RootOf(_Z^3-_Z^2-2*_Z+1))
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MAPLE
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spec := [S, {S=Prod(Sequence(Prod(Union(Sequence(Z), Z), Z)), Union(Z, Z))}, unlabeled ]: seq(combstruct[count ](spec, size=n), n=0..20);
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CROSSREFS
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Equals 2 * A006356(n-2), n>1.
Sequence in context: A035615 A115962 A019311 this_sequence A088219 A027375 A059727
Adjacent sequences: A052991 A052992 A052993 this_sequence A052995 A052996 A052997
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KEYWORD
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easy,nonn
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AUTHOR
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encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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EXTENSIONS
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More terms from James A. Sellers (sellersj(AT)math.psu.edu), Jun 05 2000
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