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Search: id:A052975
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| A052975 |
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A simple regular expression. |
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+0
3
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| 1, 2, 6, 19, 61, 197, 638, 2069, 6714, 21794, 70755, 229725, 745889, 2421850, 7863641, 25532994, 82904974, 269190547, 874055885, 2838041117, 9215060822, 29921113293, 97153242650, 315454594314, 1024274628963, 3325798821581
(list; graph; listen)
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OFFSET
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0,2
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COMMENT
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Number of (s(0), s(1), ..., s(2n)) such that 0 < s(i) < 7 and |s(i) - s(i-1)| = 1 for i = 1,2,....,2n, s(0) = 3, s(2n) = 3. - Herbert Kociemba (kociemba(AT)t-online.de), Jun 11 2004
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LINKS
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INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 1047
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FORMULA
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G.f.: -(-1+2*x)*(-1+x)/(-1+5*x-6*x^2+x^3)
a(n)=A028495(2n). - Floor van Lamoen (fvlamoen(AT)hotmail.com), Nov 02 2005
Sum(1/7*(2-3*_alpha+_alpha^2)*_alpha^(-1-n), _alpha=RootOf(-1+5*_Z-6*_Z^2+_Z^3))
a(n)=(2/7)*Sum(r, 1, 6, Sin(r*3*Pi/7)^2(2Cos(r*Pi/7))^(2n)); a(n) = 5a(n-1)-6a(n-2)+a(n-3). - Herbert Kociemba (kociemba(AT)t-online.de), Jun 11 2004
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MAPLE
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spec := [S, {S=Sequence(Prod(Union(Sequence(Prod(Sequence(Z), Z)), Sequence(Z)), Z))}, unlabeled ]: seq(combstruct[count ](spec, size=n), n=0..20);
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CROSSREFS
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Cf. A060557.
Adjacent sequences: A052972 A052973 A052974 this_sequence A052976 A052977 A052978
Sequence in context: A014010 A022015 A138747 this_sequence A035929 A071646 A114627
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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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