

A117613


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 collinear cubes).


0



0, 0, 1, 8, 22, 256, 2247, 21576, 225102, 2303014, 24563283, 267169300, 2937239494, 32814269626, 370231763542, 4215902111928
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OFFSET

0,4


COMMENTS

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.


LINKS

Table of n, a(n) for n=0..15.
Richard Gordon, Martin M. Hanczyc, Nikolai D. Denkov, Mary A. Tiffany, Stoyan K. Smoukov, "Emergence of Polygonal Shapes in Oil Droplets and Living Cells: The Potential Role of Tensegrity in the Origin of Life", Habitability of the Universe before Earth, Vol. 1 of the series Astrobiology: Exploring Life on Earth and Beyond, first edition, Richard Gordon, Alexei A. Sharov editors, Elsevier, 2017, p. 487.


CROSSREFS

Sequence in context: A131622 A217275 A183308 * A215740 A304177 A306834
Adjacent sequences: A117610 A117611 A117612 * A117614 A117615 A117616


KEYWORD

nonn,more


AUTHOR

John Tromp, Apr 06 2006


EXTENSIONS

a(15) from John Tromp, May 05 2006


STATUS

approved



