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Search: id:A052923
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| A052923 |
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A simple regular expression. |
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+0
3
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| 1, 0, 4, 4, 20, 36, 116, 260, 724, 1764, 4660, 11716, 30356, 77220, 198644, 507524, 1302100, 3332196, 8540596, 21869380, 56031764, 143509284, 367636340, 941673476, 2412218836, 6178912740, 15827788084, 40543439044, 103854591380
(list; graph; listen)
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OFFSET
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0,3
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LINKS
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INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 908
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FORMULA
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G.f.: (-1+x)/(-1+x+4*x^2)
Recurrence: {a(1)=0, a(0)=1, 4*a(n)+a(n+1)-a(n+2)}
Sum(1/17*(-1+9*_alpha)*_alpha^(-1-n), _alpha=RootOf(-1+_Z+4*_Z^2))
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MAPLE
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spec := [S, {S=Sequence(Prod(Sequence(Z), Z, Union(Z, Z, Z, Z)))}, unlabeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
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Cf. A006131, A026581.
Sequence in context: A087213 A117857 A165559 this_sequence A014433 A072696 A075219
Adjacent sequences: A052920 A052921 A052922 this_sequence A052924 A052925 A052926
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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 06 2000
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