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Wythoff's Game


Wythoff's game is a two-player game with two heaps whose sizes are nonnegative integers. A player must take a positive number of counters from either heap or the same positive number from both, and the player taking the last counter wins. With the smaller heap first, the safe combinations are (x,x+r) for integers r>=0, where x=|_phir_|, with phi the golden ratio and |_x_| the floor function. It is also true that x+r=|_phi^2r_|. The first few nonzero safe combinations are (1, 2), (3, 5), (4, 7), (6, 10), ... (OEIS A000201 and A001950), which are the pairs of elements from the complementary Beatty sequences for phi and phi^2 (Wells 1986, p. 40).

The remoteness R(x,y) counts the number of moves when the winning player wins as quickly as possible and the losing player delays defeat as long as possible. For 0<=x<=y, Sánchez Galán and Xu (2026) proved

 R(x,y)=2min{iota(x),y-x}+epsilon(x,y),

where iota(0)=0 and, for x>0, iota(x) is the unique positive integer m with x=|_mphi_| or x=|_mphi^2_|. Also, epsilon(x,y)=0 when x=|_phi(y-x)_|, and epsilon(x,y)=1 otherwise. This extends the losing-position remoteness values of Boros et al. (2024) to every position. Sánchez Galán and Xu (2026) report ChatGPT assistance with writing the supplementary verification code.


See also

Beatty Sequence, Nim, Safe, Wythoff Sequence

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References

Ball, W. W. R. and Coxeter, H. S. M. Mathematical Recreations and Essays, 13th ed. New York: Dover, pp. 39-40, 1987.Bogomolny, A. "Wythoff's Nim." https://cut-the-knot.org/pythagoras/withoff.shtml.Boros, E.; Gurvich, V.; Makino, K.; and Vyalyi, M. "Computing Remoteness Functions of Moore, Wythoff, and Euclid's Games." Internat. J. Game Theory 53, 1315-1333, 2024. https://doi.org/10.1007/s00182-024-00914-2.Coxeter, H. S. M. "The Golden Section, Phyllotaxis, and Wythoff's Game." Scripta Math. 19, 135-143, 1953.O'Beirne, T. H. Puzzles and Paradoxes. Oxford, England: Oxford University Press, pp. 109 and 134-138, 1965.Sánchez Galán, R. and Xu, Y. "A Remoteness Formula for Generalized Wythoff Games." 21 Oct 2026. https://arxiv.org/abs/2610.30427.Sloane, N. J. A. Sequences A000201/M2322 and A001950/M1332 in "The On-Line Encyclopedia of Integer Sequences."Wells, D. The Penguin Dictionary of Curious and Interesting Numbers. Middlesex, England: Penguin Books, p. 40, 1986.Wythoff, W. A. "A Modification of the Game of Nim." Nieuw Arch. Wisk. 8, 199-202, 1907/1909.

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Wythoff's Game

Cite this as:

Weisstein, Eric W. "Wythoff's Game." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/WythoffsGame.html

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