Stones in cups

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Stones in cups
Cipra's problem 1388
© 1992, Barry Cipra
USA
Published rules
This game is a solitaire
One cycle
Multiple lap
n holes per row
One row

Stones in Cups, also called Cipra's Problem 1388, is a solitaire mancala game. Closely related games are circular composition and montreal solitaire. The game was invented in 1992 by Barry Cipra, a resident of Northfield, Minnesota (USA), who proposed it as a mathematical problem in Mathematics Magazine. The game was independently solved by Kay P. Litchfield (Farmington, Utah, USA) and David Callan (University of Wisconsin, Madison, USA) in 1993. The solutions use inverse moves, that is reverse sowing. The game was also briefly described by Paul J. Campbell and Darrah P. Chavey in 1995.

Contents

Rules

The game is played with n cups that are arranged in a circle. At the beginning there are k stones placed in each cup.

board
Possible set-up

The first move may start from any cup. Later, a move begins at the cup, which was filled last. It is, as some sort of multiple lap, but also continuing the sowing with a singleton.

Each move the contents of a cup are distributed clockwise, one by one, into the succeeding cups.

The game ends when all the stones wind up in the original cup. The next move would restore the original position. The number of steps to reach this result is called a(kn). Your task is to predict the number of steps.

Example

Let's try it with two holes and one seed per hole (k=1, n=2)

board
board
board
board
Now, all stones are in the original cup
board
And the initial position, after all stones were in the original cup, is reached after 4 steps.

You can try it for other values of k and n.

Results

The first values are given in the following table:

k\n 1 2345
1 1 4 15 12 75
2 1 6 21 164 115
3 112 45 164 260
4 1 8132 1243825
5 1 6 4815801966


References

Callan, D. & Litchfield, K. P. 
(1993) 'Stones in Cups (Solutions)', in Mathematics Magazine; 66. Pages 58-59.
Campbell, P. J. 
(1995) 'Tchuka Ruma Solitaire', in The UMAP Journal; 16 (4). Pages 343-365.
Cipra, B. 
(1992) '1388', in Mathematics Magazine; 65. Page 56.
Servedio, R. & Yeh, Y.-N. 
(1995) 'A Bijective Proof on Circular Compositions', in Bulletin of the Institute of Mathematics Academia Sinica; 23. Page 283-293.


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