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A047708 Diagonal of Sprague-Grundy function for Wyt Queens (Wythoff's game). 2
0, 2, 1, 6, 7, 8, 3, 5, 4, 16, 14, 15, 10, 9, 11, 20, 13, 21, 12, 25, 17, 18, 19, 30, 31, 38, 35, 36, 22, 23, 43, 45, 48, 49, 24, 26, 27, 28, 29, 33, 60, 32, 61, 57, 66, 37, 63, 34, 64, 67, 40, 39, 41, 42, 82, 44, 74, 79, 47, 46, 87, 86, 50, 95, 96, 52, 101, 51, 102, 53, 54 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

Since Wythoff(m,n) <= m+n, Wythoff(n,n) <= 2n. It is not known whether there is an efficient (linear in log(m)+log(n)) strategy to compute Wythoff(m,n). Each single row is "easy" in the sense that a+n-Wythoff(a,n) is eventually periodic. - Howard A. Landman.

Inverse of sequence A048850 considered as a permutation of the nonnegative integers. - Howard A. Landman, Sep 25 2001

Comments from Howard A. Landman, Nov 24 2007 (Start): It is impossible for any integer to appear twice in this sequence because of the way it is constructed. Thus to prove that it is a permutation of the integers, we need only show that every value g appears at least once.

Suppose this was not true; then there must be some g such that for any value of n, G(n,n) is not = g. Since G(n,n) is defined as the smallest number not found as a G(k,n), G(n,k), or G(k,k) for k < n, this can only happen in one of 2 ways; either there is a number g' smaller than g which is chosen (this can occur at most g times) or g already appears as both G(n,k) and G(k,n) for some k < n (because G(n,k) = G(k,n)) (this can happen at most n/2 times).

Thus we have n <= n/2 + g, or n <= 2g; if g has not appeared within the first 2g terms we have a contradiction. Therefore not only must every integer g appear in the sequence, but it must appear within the first 2g terms (and no sooner than term g/2, since G(n,n) <= 2n). Conversely, this also proves that n/2 <= A(n) = G(n,n) <= 2n. (End)

REFERENCES

E. R. Berlekamp, J. H. Conway and R. K. Guy, Winning Ways, Academic Press, NY, 2 vols., 1982, see p. 76.

Howard A. Landman, "A Simple FSM-Based Proof of the Additive Periodicity of the Sprague-Grundy Function of Wythoff's Game", in R. Nowakowski (ed.), More Games of No Chance.

Howard A. Landman and Tom Ferguson showed that this is a permutation of the integers at the Jul 24-28 2000 MSRI workshop on combinatorial games.

Wythoff, W. A. ``A Modification of the Game of Nim.'' Nieuw Arch. Wiskunde 8, 199-202, 1907/1909.

LINKS

Table of n, a(n) for n=0..70.

H. S. M. Coxeter, The Golden Section, Phyllotaxis and Wythoff's Game, Scripta Math. 19 (1953), 135-143. [Annotated scanned copy]

A. Dress, A. Flammenkamp and N. Pink, Additive periodicity of the Sprague-Grundy function of certain Nim games, Adv. Appl. Math., 22, p. 249-270 (1999).

Index entries for sequences that are permutations of the natural numbers

MATHEMATICA

mex[list_] :=  mex[list] = Min[Complement[Range[0, Length[list]], list]];

move[Wnim, {a_, b_}] :=  move[Wnim, {a, b}] =

   Union[Table[{i, b}, {i, 0, a - 1}], Table[{a, i}, {i, 0, b - 1}],

    Table[{a - i, b - i}, {i, 1, Min[a, b]}]];

SpragueGrundy[game_, list_] :=  SpragueGrundy[game, list] =

   mex[SpragueGrundy[game, #] & /@ move[game, list]];

Table[SpragueGrundy[Wnim, {i, i}], {i, 0, 64}] (* Birkas Gyorgy, Apr 19 2011 *)

CROSSREFS

Main diagonal of square array in A004481. Sequences A000201 and A001950 give the m and n coordinates of the zeros of Wythoff (i.e. the P-positions of the game, where the previous player has won).

Cf. A048850.

Sequence in context: A196554 A244647 A160348 * A256277 A252746 A182883

Adjacent sequences:  A047705 A047706 A047707 * A047709 A047710 A047711

KEYWORD

nonn,easy,nice

AUTHOR

N. J. A. Sloane

EXTENSIONS

More terms from Howard A. Landman

STATUS

approved

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Last modified July 21 17:51 EDT 2017. Contains 289643 sequences.