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Search: id:A052540
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| A052540 |
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A simple regular expression. |
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+0
1
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| 1, 1, 2, 5, 10, 21, 45, 95, 201, 426, 902, 1910, 4045, 8566, 18140, 38415, 81351, 172276, 364827, 772590, 1636105, 3464761, 7337285, 15538085, 32904826, 69682176, 147565152, 312497045, 661771440, 1401425856, 2967783605
(list; graph; listen)
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OFFSET
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0,3
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COMMENT
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Equals INVERT transform of (1, 1, 2, 1, 1, 1,...). [From Gary W. Adamson (qntmpkt(AT)yahoo.com), Apr 27 2009]
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LINKS
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INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 472
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FORMULA
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G.f.: -(-1+x)/(1-2*x-x^3+x^4)
Recurrence: {a(1)=1, a(0)=1, a(3)=5, a(2)=2, a(n)-a(n+1)-2*a(n+3)+a(n+4)}
Sum(-1/643*(-94-127*_alpha-22*_alpha^2+75*_alpha^3)*_alpha^(-1-n), _alpha=RootOf(1-2*_Z-_Z^3+_Z^4))
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MAPLE
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spec := [S, {S=Sequence(Prod(Z, Union(Prod(Z, 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: A114279 A101400 A131403 this_sequence A018106 A151497 A110744
Adjacent sequences: A052537 A052538 A052539 this_sequence A052541 A052542 A052543
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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 05 2000
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