# Questions tagged [recreational-mathematics]

Applications of mathematics for the design and analysis of games and puzzles

269 questions
Filter by
Sorted by
Tagged with
143 views

### Inspired by a card game: finding a path through $[\mathbb{N}]^n$

Motivation. Today my sons played a card game, in which a fixed number $n$ of cards was lying on the table. A move consists of adding an unused card to the cards on the table, and removing a card from ...
499 views

### Optimal schedule for a soccer tournament

Motivation. This weekend, my children took part in a soccer tournament consisting of $n$ teams, each of which playing once against every other team. As there was only one soccer field, the schedule ...
77 views

### Parity of 4×4 normal magic squares

I'm writing a program that given an integer n returns all normal magic squares of size n × n. Fiddling around with it a little I started to notice that if n equals 4, every square I saw followed this ...
188 views

### What does the best die look like?

Intransitive dice have attracted a lot of attention - especially in the context of recreational math - since their introduction by Efron in the 1960s. More recently, there has been work studying ...
237 views

### Has there been any progress on Conway's and Soifer's shortest paper?

In 2005 Conway and Soifer published the famous shortest ever paper, asking whether an equilateral triangle of sidelength $n+\varepsilon$ can be covered by $n^2+1$ unit equilateral triangles and ...
1 vote
80 views

### Eventual stabilization for repeatedly adding multiplayer games

This question is an outgrowth of a couple previous questions of mine. In order: 1,2,3. This should be fully self-contained, but those questions may help motivate this one. To keep things readable, I'...
133 views

### Can we arrange {1,...,9} in 3×3 grid so the set of products of rows equals the set of products of columns? [closed]

I find a interesting question of Prmo mock and Promys 2020 For which $n\in\mathbb{N}$ is it possible to arrange $\{1,…,n^2\}$ in an $n\times n$ grid so that the set of products of columns equals the ...
200 views

### Monoid associated to $>2$-player Hackenbush

There is some literature on multiplayer combinatorial game theory, but as far as I can tell none of it follows the line of attack below. I'd love a pointer to a similar approach taken in the ...
218 views

### For which $n$ does a y-formed $n$-polyomino tile a $n \times n \times n$-cube?

I got from my children as a gift a puzzle consisting of 25 y-shaped 5-polyominoes that form a $5 \times 5 \times 5$-cube (see picture). I'm wondering for which $n$ does a y-formed $n$-polyomino tile a ...
458 views

### Scheduling "parent talks" at school

Real life motivation. In my younger son's class, there are $18$ students. His teacher provided $18$ time slots for the parents of each child to have a 30-minute conversation of their kid's progress in ...
460 views

### Are there journals for "fun mathematics"?

Are there peer-reviewed journals that focus on "fun mathematics"? By this I mean fun things that do involve nontrivial mathematics and which I think other mathematicians would enjoy reading ...
668 views

### The $9$th tetration of $-\sqrt2$

Let $^na$ denote the $n$th tetration of $a$, so that $^0a=1$ and $$^{n+1}a=a^{^na}$$ for $n=0,1,\dots$. (For complex $x$ and $y$, here we use the definition $x^y:=e^{y\ln x}$, where $\ln$ is the ...
153 views

### Transitive action on domino tilings

Fix a $n \times m$ rectangle and consider the set $S_{n,m}$ of all its dominos tilings. Here are examples with $n=m=8$. The set $S_{n,m}$ is empty if and only if $nm$ is odd, and for small $nm$, its ...
1 vote
146 views

### Another Goldbach variation for odd numbers?

Lemoine's conjecture (also called Levy's conjecture according to Professor Wikipedia) states that every odd integer larger than $5$ is the sum of a prime and of twice a prime. Dabbling in the dark art ...
1 vote
93 views

1k views

1 vote
105 views

### Wrapping Wallpapers around Surfaces

I am intrigued by my honey bottle. Its neck is neatly wrapped by (almost) hexagons. I checked and there are no such things as part-hexagons, quarter-hexagons, half-hexagons, etc. -- if you have seen ...
106 views

215 views

### Name of a game : Remove two chips from a vertex or one chip from both ends of an edge

Consider a finite graph $\Gamma$ with a positive number $n_v\geq 0$ of chips stacked at each vertex $v$ of $\Gamma$. Two players play in turn with moves consisting either of removing two chips from a ...
754 views

### Can the thief escape (from a smooth, simple closed curve)?

Let $C\subset \mathbb{R}^2$ be a smooth, simple closed curve. The thief is inside $C$. Before he starts to move, the police bureau of the $\mathbb{R}^2$ world can freely place countably infinite ...
863 views

### Who wins this two player game of making squares?

Two players take turns coloring edges on an $n$-by-$n$ grid. Both players use the same color. Every time a player surrounds a square of the grid, they mark that square with their name and go again. ...
187 views

### Distribution of stopping time for a 2D random walk

Consider the following process on $\mathbb{C}$: Start at the point 1. At each step, move by adding $e^{i\theta}$, where $\theta$ is uniformly drawn from $\mathbb{S}^1$. Stop at the first positive ...
519 views

### Can the theory of elliptic functions developed from purely geometric considerations?

I always had this question, but was unable to get a definitive answer to it. There is the theorem of division of the arc length of the lemniscate with ruler and compass. So I always wondered, is it ...
599 views

### The devil's playground

On the $\mathbb{R}^2$ plane, the devil has trapped the angel in an equilateral triangle of firewalls. The devil starts at the apex of the triangle. can move at speed $1$ to leave a trajectory of ...
474 views

Motivation. (Please skip if you are not in the mood for "chitchat".) Last night I listening to a classical radio station, and for the umpteenth time, they played Mendelssohn's Psalm 42, a ...
236 views

### Putting $\omega$ in two boxes

Motivation. My eldest son starts school tomorrow. His class is split in two groups of $10$ students each. From time to time, the groups are rearranged. I wondered how many rearrangements are needed ...
We are given an integer $n \geq 1$ and $2n$ cards, labelled $0$ to $2n-1$. We pick a card with uniform probability, put it back, and continue, until for some $k\in \{0,n-1\}$ the cards $2k$ and $2k+1$ ...
Consider a random work on $L=\mathbb Z^2$ endowed with obstacles (i.e each cell $(x,y)$ of $L$ may contain a obstacle, i.e the random walk halts whenever it hits such a cell). Let $P(x,y) = 1$ if cell ...