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Search: id:A052939
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| A052939 |
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A simple regular expression. |
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+0
3
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| 1, 3, 9, 28, 87, 271, 844, 2629, 8189, 25508, 79455, 247495, 770924, 2401357, 7480005, 23299524, 72575863, 226067103, 704178124, 2193449749, 6832393165, 21282272996, 66292312655, 206494424631, 643211040556, 2003542920989
(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 930
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FORMULA
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G.f.: -(-1+x^2)/(1-3*x-x^2+2*x^3)
Recurrence: {a(0)=1, a(1)=3, 2*a(n)-a(n+1)-3*a(n+2)+a(n+3), a(2)=9}
Sum(-1/229*(-66-15*_alpha+28*_alpha^2)*_alpha^(-1-n), _alpha=RootOf(1-3*_Z-_Z^2+2*_Z^3))
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MAPLE
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spec := [S, {S=Sequence(Union(Z, Z, Prod(Z, Sequence(Prod(Z, Z)))))}, unlabeled ]: seq(combstruct[count ](spec, size=n), n=0..20);
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CROSSREFS
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Sequence in context: A091140 A052541 A024738 this_sequence A085839 A134915 A115239
Adjacent sequences: A052936 A052937 A052938 this_sequence A052940 A052941 A052942
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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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