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Search: id:A052543
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| A052543 |
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A simple regular expression. |
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+0
1
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| 1, 2, 8, 26, 90, 306, 1046, 3570, 12190, 41618, 142094, 485138, 1656366, 5655186, 19308014, 65921682, 225070702, 768439442, 2623616366, 8957586578, 30583113582, 104417281170, 356502897518, 1217177027730, 4155702315886
(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 478
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FORMULA
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G.f.: -(-1+x)/(1-3*x-2*x^2+2*x^3)
Recurrence: {a(0)=1, a(1)=2, a(2)=8, 2*a(n)-2*a(n+1)-3*a(n+2)+a(n+3)}
Sum(-1/98*(-13-25*_alpha+16*_alpha^2)*_alpha^(-1-n), _alpha=RootOf(1-3*_Z-2*_Z^2+2*_Z^3))
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MAPLE
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spec := [S, {S=Sequence(Prod(Union(Z, Z), Union(Z, Sequence(Z))))}, unlabeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
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Sequence in context: A060410 A128634 A053956 this_sequence A026638 A067855 A129368
Adjacent sequences: A052540 A052541 A052542 this_sequence A052544 A052545 A052546
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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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