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Rubik's Clock


Rubik's Clock is a puzzle consisting of 18 small clocks, 14 of which are independent, each of which may be set to any 12-hour position. A configuration records only clock-hand positions, giving 12^(14) possible configurations. One move turns a wheel by any nonzero number of hours, with the four pins selecting which clocks move. Changing the pins costs no move. The God's number (i.e., the graph diameter of the graph corresponding to Rubik's Clock, which is the minimum number of moves required to solve it from an arbitrary starting position-i.e., in the worst case) was shown by Kogler to be 12 (Kogler 2014; cube20.org).

The numbers of positions requiring exactly n=0, 1, ..., 12 moves in a shortest solution are 1, 330, 51651, 4947912, 317141342, 14054473232, 428862722294, 8621633953202, 101600180118726, 528107928328516, 613251601892918, 31893880879492, and 39248 (OEIS A256586; cube20.org), which sum to 12^(14) as they must.


See also

God's Number, Rubik's Cube

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References

cube20.org. "Rubik's Clock Has Now Been Solved!" https://www.cube20.org/clock/.Dénes, J. and Mullen, G. L. "Rubik's Clock and Its Solution." Math. Mag. 68, 378-381, 1995. https://doi.org/10.1080/0025570X.1995.11996360.Kogler, J. "God's Number for Clock Found." May 31, 2014. https://www.speedsolving.com/threads/gods-number-for-clock-found.47822/.Scherphuis, J. "Jaap's Puzzle Page: Rubik's Clock." https://www.jaapsch.net/puzzles/clock.htm.Sloane, N. J. A. Sequence A256586 in "The On-Line Encyclopedia of Integer Sequences."Zeilberger, D. "Doron Zeilberger's Maple Packages and Programs: RubikClock." https://sites.math.rutgers.edu/~zeilberg/programs.html.

Referenced on Wolfram|Alpha

Rubik's Clock

Cite this as:

Weisstein, Eric W. "Rubik's Clock." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/RubiksClock.html

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