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Search: id:A117613
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| A117613 |
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The number of 3D configurations of a labeled size 2*n "wurfel". A wurfel consists of a series of cubes held together on a looped string such that the string makes a right angle inside each cube. Ignoring the labels would make a wurfel a special kind of polycube in which the cubes can be cyclically ordered at consecutive right angles (equivalently, avoiding 3 consecutive colinear cubes). |
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+0
1
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| 0, 0, 1, 8, 22, 256, 2247, 21576, 225102, 2303014, 24563283, 267169300, 2937239494, 32814269626, 370231763542, 4215902111928
(list; graph; listen)
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OFFSET
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0,4
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COMMENT
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a(2)=1 since a loop of 2*2=4 labeled cubes has only 1 possible 3D shape. A C program for computing the sequence is available on request.
Richard Gordon from the University of Manitoba (GordonR(AT)ms.umanitoba.ca) first raised the question of how many wurfels there are.
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CROSSREFS
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Sequence in context: A033456 A026593 A131622 this_sequence A109271 A029755 A022420
Adjacent sequences: A117610 A117611 A117612 this_sequence A117614 A117615 A117616
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KEYWORD
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nonn
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AUTHOR
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John Tromp (tromp(AT)cwi.nl), Apr 06 2006
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EXTENSIONS
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a(15) from John Tromp (tromp(AT)cwi.nl), May 05 2006
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