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Search: id:A052931
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| A052931 |
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A simple regular expression. |
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+0
4
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| 1, 0, 3, 1, 9, 6, 28, 27, 90, 109, 297, 417, 1000, 1548, 3417, 5644, 11799, 20349, 41041, 72846, 143472, 259579, 503262, 922209, 1769365, 3269889, 6230304, 11579032, 21960801, 40967400, 77461435, 144863001, 273351705, 512050438
(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 917
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FORMULA
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G.f.: -1/(-1+3*x^2+x^3)
Recurrence: {a(1)=0, a(0)=1, a(2)=3, a(n)+3*a(n+1)-a(n+3)}
Sum(1/9*(-1+5*_alpha+2*_alpha^2)*_alpha^(-1-n), _alpha=RootOf(-1+3*_Z^2+_Z^3))
a(n)=sum{k=0..floor(n/2), binomial(k, n-2k)3^(3k-n)} - Paul Barry (pbarry(AT)wit.ie), Oct 04 2004
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MAPLE
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spec := [S, {S=Sequence(Prod(Z, Union(Z, Z, Z, Prod(Z, Z))))}, unlabeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
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Adjacent sequences: A052928 A052929 A052930 this_sequence A052932 A052933 A052934
Sequence in context: A105545 A027465 A127552 this_sequence A006803 A019770 A136320
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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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