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Enumerative combinatorics, graph theory, order theory, posets, matroids, designs and other discrete structures. It also includes algebraic, analytic and probabilistic combinatorics.
16
votes
0
answers
976
views
A Combinatorial Game: the Snake and the Hunter
The Snake and the Hunter is a game for two players who play in two rounds interchanging the roles of snake and hunter. The game is played in a rectangular grid of points, say $6 \times 6$. In both rou …
15
votes
2
answers
882
views
Lattice n-gons with ordered side lengths 1,2,3,...,n
Consider the octagon in the Cartesian plane with vertices at (0,0), (1,0), (1,2), (4,2), (4,6), (7,2), (7,8), and (0,8).
Are there other (infinitely many) polygons, such as this, lying entirely in the …
9
votes
2
answers
1k
views
A property of 47 with respect to partitions into five parts
Is 47 the largest number which has a unique partition into five parts (15, 10, 10, 6, 6), no two of which are relatively prime?
9
votes
1
answer
250
views
Finding the largest number which cannot be the sum of the labels of the Petersen graph
The vertices of the Petersen graph (or any other simple graph) can be labelled in infinitely many ways with positive integers so that two vertices are joined by an edge if, and only if, the correspond …
9
votes
1
answer
348
views
A Combinatorial Game with Integer Sequences
Two players, Alice and Bob, take turns constructing a sequence $a_1,a_2,a_3,\dots$, of distinct positive integers, none greater than a given parameter $K$. Alice plays first and makes $a_1=1$. Thereaf …
7
votes
3
answers
977
views
Tiling a square with rectangles whose areas or perimeters are 1, 2, 3, ..., N
For which positive integers N does there exist a square that can be completely tiled with N rectangles of integer sides whose areas or perimeters are precisely 1, 2, 3, ..., N?
6
votes
6
answers
1k
views
Least number of vertices in a graph with which one can uniquely recover some partition of N
Given a partition of an integer $N$, its $P$-graph is the graph whose vertices are its parts, two of which are joined by an edge if and only if they have a common divisor greater than one (i.e. they a …
5
votes
0
answers
155
views
Tiling rectangles using all squares of sides 1, 2, 3, ..., n
Do integers n greater than 2 exist such that all the squares of sides 1, 2, 3, ..., n can be partitioned into two or more sets (none a singleton) each of whose squares can be used to tile a rectangle? …
5
votes
1
answer
247
views
Dealing cards numbered $1$ to $n$ into piles
Is anything known about the following?
I hold in my hand a shuffled pack of cards numbered $1$ to $n$. One by one, I place them all, face up, on a table in piles. For each card I deal from my hand, sa …
4
votes
0
answers
145
views
Tiling squares with oblongs
An oblong is a rectangle whose width and length are consecutive integers: 1x2, 2x3, 3x4, etc. Does N exist such that it is possible to split the first N oblongs into 2 or more non-intersecting sets so …
4
votes
0
answers
229
views
A property of the partitions of 311 with regard to the divisors of its parts
Given a multiset of positive integers, its P-graph is the loopless graph whose vertex set consists of those integers, any two of which are joined by an edge if they have a common divisor greater than …
4
votes
Least number of vertices in a graph with which one can uniquely recover some partition of N
Freddy Barrera has shown that $k(1000)>5$ by verifying that every graph with fewer than 6 vertices (other than the singleton) is the P-graph of at least two partitions of 1000. On the other hand, from …
2
votes
0
answers
229
views
Generating all graphs of order 4 with the help of Collatz
Given a set of positive integers, its common divisor graph ( CD-graph) is the graph whose vertices are the integers, two of which are joined by an edge if (and only if) they have a common divisor grea …
2
votes
1
answer
212
views
Are there graphs for which infinitely many numbers cannot be the sum of the labels of its ve...
The vertices of any simple graph can be labeled in infinitely many ways with positive integers so that two vertices are joined by an edge if, and only if, they have a common divisor greater than 1.
…
2
votes
2
answers
225
views
Generating all pentominoes by cutting and pasting
Is it possible to place the twelve pentominoes around a circle in such a way that if two of the pentominoes find themselves next to each other, it is because one of the two can be obtained from the ot …