


Game Theory / Number Theory
Org: Richard Nowakowski (Dalhousie), Bill Sands (Calgary), Hugh Williams (Calgary) and Robert Woodrow (Calgary) [PDF]
 MIKE BENNETT, University of British Columbia, Vancouver, BC
The prime factorization of binomial coefficients
[PDF] 
Let us suppose that n and k are positive integers with n ³ 2k, and factor the binomial coefficient \binomnk = U ·V,
where U is comprised of those primes not exceeding k and V
contains those primes exceeding k. Then an old theorem of Ecklund,
Eggleton, Erdös and Selfridge asserts that V > U, with at most
finitely many exceptions (all of which are conjectured to be known).
We will take a rather different approach to this problem than that of
Ecklund, Eggleton, Erdös and Selfridge, enabling us to resolve
their conjecture in two of the three remaining cases.
This is joint work with M. Filaseta and O. Trifonov.
 ELWYN BERLEKAMP, University of California, 2039 Shattuck Ave, Berkeley, CA 94704
YellowBrown Hackenbush
[PDF] 
YellowBrown Hackenbush is a game played on a sum of strings whose
branches are colored yellow or brown. In its "restricted" form, one
player, named Left, at her turn, picks a bichromatic string and
removes its highest yeLLow branch. Right, at his turn, picks a
bichromatic string and removes its highest bRown branch. As in the
wellknown game of bLueRed Hackenbush, all higher branches, being
disconnected, also disappear. But in yellowbrown Hackenbush, unlike
bluered Hackenbush, all moves on monochromatic strings are illegal.
This makes all values of yellowbrown Hackenbush allsmall.
This paper presents an explicit solution of restricted yellowbrown
Hackenbush. The values are sums of basic infinitesimals that have
appeared in many other games found in Winning Ways and elsewhere.
 PETER BORWEIN, Simon Fraser University
Littlewood's 22nd Problem
[PDF] 
Littlewood, in his 1968 monograph "Some Problems in Real and Complex
Analysis", poses the following research problem, which appears to
still be open:
"If the n_{m} are integral and all different, what is the lower bound
on the number of real zeros of
Possibly N1, or not much less."
No progress appears to have been made on this in the last half
century. Until now!
 DAVID BOYD, University of British Columbia, Vancouver, BC
Pisot sequences with periodic rounding rules
[PDF] 
The classical Pisot sequence E(a_{0},a_{1}) is defined by the nonlinear
recurrence a_{n+2} = N(a_{n+1}^{2}/a_{n}), where a_{0} < a_{1} are
positive integers and N(x) means round x to the nearest integer.
One can define a variety of different sequences by replacing N(x) by
U(x) or D(x) where these mean round x up or down to the closest
integer, respectively. Here we consider rounding rules which apply
the operators U and D in a periodic fashion, e.g. the
sequence UUDUD(a_{0},a_{1}) would start by rounding up for the
next two rounds, then down, then up, then down, repeating this
indefinitely. One is interested in subset of such sequences which
satisfy linear recurrence relations. We show that there is a striking
difference between the case in which the rounding rule has minimal
period at most 2, and the case in which this period is greater than
2. The results have some applications to questions about classical
Pisot sequences.
 ANDREW BREMNER, Arizona State University, Tempe, AZ 852871804, USA
A problem in right triangles
[PDF] 
We investigate the following problem mentioned in Dickson's History,
Vol. 2, Chapter 4, on rational right triangles (evidently it was posed
in obscure verse in The Ladies Diary for 1728 as Question 133, but
seems to be based on a numerical example of Ozanam from 1702):
Find a right triangle each of whose sides exceeds double the area by a
square.
We analyze the mathematics behind the problem, and inter alia
find an example with smallest possible standard generators for the
underlying Pythagorean triangle.
The observation is also made that mathematicians whose names are
anagrams of rivers seem to be particularly scarce.
 DENIS CHARLES, Microsoft Research
Some applications of the graph of supersingular elliptic
curves over a finite field
[PDF] 
The graph of supersingular elliptic curves over a finite field
connected by isogenies has many applications in computational number
theory. In this talk we look at some old (in number theory) and new
(in cryptography) applications of these graphs. In particular, we
discuss new constructions of secure hash functions and pseudorandom
number generators from these graphs.
 KARL DILCHER, Dalhousie University, Halifax, Nova Scotia, B3H 3J5
Divisibility properties of certain binomial sums
[PDF] 
We study congruence and divisibility properties of a class of
combinatorial sums that involve products of powers of two binomial
coefficients, and show that there is a close relationship between
these sums and the theorem of Wolstenholme. We also establish
congruences involving Bernoulli numbers, and finally we prove that
under certain conditions the sums are divisible by all primes in
specific intervals.
This is joint work with Marc Chamberland.
 AVIEZRI FRAENKEL, Weizmann Institute of Science, Rehovot, Israel
Can one perceive the alpine wind of a game?
[PDF] 
Nim and chess are both combinatorial games with perfect information
and no chance moves. Why is Nim easy and chess hard? There are
several mathematical differences between them. Previously we have
launched a concentrated attack on each of the differences separately,
since this divideandconquer approach has a better chance of
answering our question than a direct attempt to scale the sheer cliff
separating polynomial Nim from Exptimecomplete chess. We thus
ascended from sealevel Nim towards alpineheights chess at a moderate
gradient, by gradually introducing into Nim more and more
complications in a natural order of increasing complexities. What
happens at the higher elevations, when we have already introduced
cycles and a capture rule, but games are still impartial? We will
attempt to show how one can hear and feel the breeze of the crisp
alpine wind blowing out of such games. The talk is dedicated to
Richard Guy, who is both a leading gamester and a keen member of the
Alpine Club of Canada; both of these activities made him 90 years
young!
 CARL POMERANCE, Dartmouth College, Hanover, NH 03755, USA
Covering congruences
[PDF] 
Over 50 years ago, Paul Erdös conjectured that the integers can be
covered by a finite collection of residue classes a_{i} mod n_{i} with
distinct moduli n_{i}, and with the least modulus arbitrarily large.
So far, the record is due to Morikawa in 1984, who has found such a
covering system with least modulus 24. This, and similar problems,
are discussed extensively in Guy's UPINT. We solve one of these
problems, namely, we prove the conjecture of Erdös and Selfridge
that in a covering system with large least modulus, the reciprocal sum
of the moduli must also be large. In addition, we prove the
conjecture of Erdös and Graham that for each K > 1, there is a
positive number d_{K} such that if the moduli all come from an
interval [N,KN], where N is large, then for any choice of residue
classes for these moduli, at least density d_{K} of the integers
remain uncovered.
This work is joint with Michael Filaseta, Kevin Ford, Sergei Konyagin,
and Gang Yu.
 RENATE SCHEIDLER, University of Calgary, Department of Mathematics,
2500 University Drive NW, Calgary, AB T2N 1N4
Units in Cubic Function Fields
[PDF] 
An efficient algorithm for computing the fundamental unit, or
equivalently, the regulator, of a real quadratic field has so far
eluded researchers. Similarly, finding the the fundamental unit(s) of
a cubic field remains computationally hard for large field sizes, and
the task only becomes messier as the degree of the field extension
increases. Interestingly, both the quadratic and the cubic scenario
employ different variants of the simple continued fraction algorithm
to generate the fundamental unit(s).
The task at hand seems to be just as hard for function fields. The
best known methods here are basically extensions of the number field
methods, but there are subtle differences which we will explain. In
this talk, we focus mainly on unit computation in cubic function
fields. We explain how to determine the unit rank of such an extension
and how to find a system of fundamental units using an extension of
Voronoi's algorithm. One of the main obstacles to efficient unit
computation is the huge size of the fundamental unitsthey are
generally exponential in the size of the fieldso as a matter of
curiosity, we also provide parameterized families of purely cubic
function fields with unusually small fundamental units.
 AARON SIEGEL, Mathematical Sciences Research Institute
The Misère Mex Mystery
[PDF] 
Under the normal play condition on an impartial game, the
player who makes the last move wins. Under the misère play
condition, whoever makes the last move loses. It was long ago
observed that misère games are vastly more difficult than their
normal counterparts.
It was also observed that in the case of Nim, there is a curious
correspondence. The strategy for misère Nim is: Follow the strategy
for normal Nim until your move would leave no heaps of size greater
than one. Then play to leave an odd number of heaps of size
one.
We will show that this correspondence generalizes to many misère
games, including many two and threedigit octals. For each such game
G, the strategy for misère G is: Follow the strategy
for normal G as long as the position remains sufficiently rich,
in a sense that depends on G. Then pay attention to the fine
structure of the misère quotient.
This broad strategic principle manifests itself in certain structural
properties of the misère quotient of G, and is tied to deep
questions about how the mex rule generalizes to misère play. We
will discuss this relationship and raise a number of intriguing
conjectures.
This is joint work with Thane Plambeck.
 DAVID SINGMASTER, 87 Rodenhurst Road, London, SW4 8AF, UK
17 Camels, 13 Camels, 11 Bridges, 3 Rabbits, Coconuts
[PDF] 
Despite its age and simplicity, recreational mathematics constantly
presents topics for historical and mathematical investigation. The
problem of the 17 camels is often claimed to be ancient, but the
earliest known example is from 1872. The 13 camels variant is only
known from one author, in 1971. Mathematical investigation determines
all possible forms of these problems for small families and finds some
extended pseudosolutions.
I will then give some brief descriptions of work on the 11 [sic!]
bridges of Konigsberg, the puzzle of the Three Rabbits [How do you
draw three rabbits, each with two ears, but using only three ears in
all?], the Monkey and the Coconuts as done by Lewis Carroll,
etc.
 ALF VAN DER POORTEN, ceNTRe for Number Theory Research, Sydney
Curious cubes and selfsimilar sums of squares
[PDF] 
I will take mild issue with Hardy's dismissive remark:
"There are just four numbers (after 1) which are the sums of the
cubes of their digits, viz. 153 = 1^{3}+5^{3}+3^{3}, 370 = 3^{3}+7^{3}+0^{3},
371 = 3^{3}+7^{3}+1^{3}, and 407 = 4^{3}+0^{3}+7^{3}. This is an odd fact,
very suitable for puzzle columns and likely to amuse amateurs, but
there is nothing in it which appeals much to a mathematician. The
proof is neither difficult nor interestingmerely a little tiresome.
The theorem is not serious; and it is plain that one reason (though
perhaps not the most important) is the extreme speciality of both the
enunciation and the proof, which is not capable of any significant
generalization."
In retaliation I nominate 1^{3}+5^{3}+3^{3} = 153, 16^{3}+50^{3}+33^{3} = 165033, 166^{3}+500^{3}+333^{3} = 166500333, 1666^{3}+5000^{3}+3333^{3} = 16665000333, ..., and turning to squares, 12^{2}+33^{2} = 1233,
88^{2}+33^{2} = 8833, .... Of course that last pair of examples is
mathematically far more interesting, and I concentrate on its
generalisation by reporting on work done some years ago jointly with
Kurt Thomsen and Mark Wiebe, at the time undergraduate students at the
University of Manitoba.
 STAN WAGON, Macalester College, St. Paul, MN 55105, USA
The postagestamp problem: an application of geometry to
number theory
[PDF] 
Given a set A of finitely many positive integers (the
denominations), the Frobenius problem comes in two flavors:
(1) determining, for a given target M, whether some
nonnegative combination of the denominations sums to M, and if so,
finding a representation;
(2) computing the Frobenius number f(A), which is the largest
M that is not representable.
For example, if A = 6, 9, 20, then f(A) = 43. The main
approaches to (2) have used graph theory and have been limited to
denominations no greater than about 10 million. We will show how a
detailed study of a certain geometrical polyhedron leads to a fast
solution that works with no restriction on the size of the
denominations.
Joint work with David Einstein, Daniel Lichtblau, and Adam Strzebonski.
 GARY WALSH, University of Ottawa, 585 King Edward St., Ottawa,
Ontario K1N 6N5
Don't try to solve these Diophantine equations
[PDF] 
Although the problem of determining all integer points on an elliptic
curve can readily be solved by any number of math packages nowadays,
it is often the case that such problems resist elementary approaches.
We will discuss just such a problem, due to Martin Gardner, along with
a related family of elliptic curves (and related Thue equations) that
continue to resist solution by any known method, elementary or not.
 DAVID WOLFE, Gustavus Adolphus College, Minnesota
Introducing New Games
[PDF] 
New games invented (or discovered) in the last few years include
Toppling Dominoes, Shove (and Push), and Maze (and Maize). These
games have simple, playable rules and include our favorite game values
such as numbers, ups and stars, but the values can appear in
surprising ways.
Work is in conjunction with Michael Albert and Richard Nowakowski.

