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 A165642 Number of ways to assemble an n-cube from 2n labeled (n-1)-cubes with labeled vertices, where left-handed and right-handed counterparts are considered distinct. 3
 2, 96, 7864320, 5917648890101760, 131757106216193173905620336640, 213712134396364787165698675955466240000000000000, 52598387159216969439004693376714880262603303706802782208000000000000000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Table of n, a(n) for n=1..7. FORMULA a(n) = 2 * ((2n-2)!!)^(2n-1) * (2n-1)! EXAMPLE For n=2, we are constructing a square from 4 labeled line-segments with labeled endpoints. Solutions which differ by a rotation are considered equivalent, but solutions which are a reflection of each other are considered distinct (assume the square we are constructing is embedded in a plane, so we cannot flip it over to convert a left-handed solution to right-handed solution). There are 6 ways to order the line-segments, and each line-segment can be oriented in 2 ways, so the total number of solutions is 6 * 2^4 = 96. For n=3, we are constructing a cube from 6 labeled squares with labeled vertices (assume we are confined to 3-space, so we consider reflections of the cube to be distinct). Without loss of generality, we can pick one labeled square to serve as our face of reference. For this face, we must decide which side of the square will face the interior of the cube, but we do not care about which rotation we pick as these just translate into rotations of the cube. From this reference square, there are 5! ways to assign the remaining squares to the faces of the cube, and each square can be oriented in 8 ways (we can pick which side of the square will face the interior of the cube, and we can pick from 4 rotations). This gives 2 * 8^5 * 5! solutions. The factor of "2" comes from the choice of which side of the reference square will face the interior of the cube (a choice which would go away if we considered reflections to be equivalent). CROSSREFS Cf. A165643 (same idea, but reflections are equivalent). A165644 and A091868 are the corresponding sequences for simplices instead of cubes. Sequence in context: A168442 A091810 A344662 * A057528 A346565 A224986 Adjacent sequences: A165639 A165640 A165641 * A165643 A165644 A165645 KEYWORD nonn AUTHOR Andrew Weimholt, Sep 23 2009 EXTENSIONS Example reformatted by Andrew Weimholt, Sep 25 2009 STATUS approved

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