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Search: id:A001444
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| A001444 |
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Bending a piece of wire of length n+1 (configurations that can only be brought into coincidence by turning the figure over are counted as different). |
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+0
5
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| 1, 2, 6, 15, 45, 126, 378, 1107, 3321, 9882, 29646, 88695, 266085, 797526, 2392578, 7175547, 21526641, 64573362, 193720086, 581140575, 1743421725, 5230206126, 15690618378, 47071677987, 141215033961
(list; graph; listen)
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OFFSET
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0,2
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COMMENT
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The wire stays in the plane, there are n bends, each is R,L or O.
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REFERENCES
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Todd Andrew Simpson, ``Combinatorial Proofs and Generalizations of Weyl's Denominator Formula,'' Ph. D. Dissertation, Penn State University, 1994.
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LINKS
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Index entries for sequences obtained by enumerating foldings
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FORMULA
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(3^n + 3^[ n/2 ] )/2.
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EXAMPLE
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There are 2 ways to bend a piece of wire of length 2 (bend it or not).
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MAPLE
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f := n->(3^floor(n/2)+3^n)/2;
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CROSSREFS
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Cf. A001997, A001998.
Sequence in context: A148439 A151515 A052870 this_sequence A138574 A045628 A127383
Adjacent sequences: A001441 A001442 A001443 this_sequence A001445 A001446 A001447
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KEYWORD
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nonn,nice,easy
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AUTHOR
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todo(AT)tasimpson.com (Todd Andrew Simpson)
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EXTENSIONS
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Interpretation in terms of bending wire from Colin Mallows (colinm(AT)research.avayalabs.com).
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