Questions tagged [recreational-mathematics]

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

Filter by
Sorted by
Tagged with
6
votes
1answer
140 views

3D Edge matching puzzle generation

I have this weird idea for a puzzle/toy (or torture device, depending on how you look at it) I've been trying to make for years now. I happen to be worse at this kind of math as I thought; and I'd be ...
0
votes
0answers
125 views

For any $n-1$ elements of $\mathbb Z/n\mathbb Z$, we can make $0$ using $\{-,+,\times\}$ without parentheses

MSE: Just using $+$ ,$-$, $\times$ using any given n-1 integers, can we make a number divisible by n? (no brackets allowed) Is there any hope in proving the following? (Cross-posted here after a ...
11
votes
1answer
399 views

“Drinking number” of a graph

Motivation. A while ago I attended a party and I only knew some, but not all, of the attendees. There were 2 kinds of drinks: beer and soda. I noticed that amongst my acquaintances, more than half ...
5
votes
1answer
1k views

How many consecutive forced moves are possible in chess?

The question concerns chess. I call a move forced if, in a given position, is the unique move consistent with the rules of the game. I wonder what is the largest integer $n$ such that there exists a ...
5
votes
1answer
219 views

Positioning ice-cream stands on a street

We want to position $n$ ice-cream stands on a street. Assume that the population on the street is modeled by a nonnegative integrable function $f$, and everyone goes to the nearest ice-cream stand. ...
5
votes
1answer
319 views

A measurable set that acts as a speedometer

Definitions and some motivation: Say a car is driving on a straight road. All we know is where it starts, and how much time it spends in certain stretches of the road. With just this much information, ...
18
votes
3answers
509 views

Tic-tac-toe with one mark type

Parameters $a,b,c$ are given such that $c\leq\max(a,b)$. In an $a\times b$ board, two players take turns putting a mark on an empty square. Whoever gets $c$ consecutive marks horizontally, vertically, ...
1
vote
2answers
265 views

Critical thinking rail track problem [closed]

On a strange railway line, there is just one infinitely long track, so overtaking is impossible. Any time a train catches up to the one in front of it, they link up to form a single train moving at ...
3
votes
1answer
141 views

Memory game inspired problem

Motivation. As I was playing the pairs-matching game "Memory" (known as "Concentration" in some parts of the world) with my children, I was surprised that even thorough shuffling ...
5
votes
1answer
165 views

Looking for a BAMS text about the group with commutation relations defined using meaningful words

What I definitely remember is that I saw a description of the following in the Bulletin of the American Mathematical Society, sometime in eighties (or maybe nineties?) One considers the group ...
3
votes
1answer
110 views

Is there a geometric way to construct $\pi \left(\frac{\alpha}{\pi}\right)\cdot\left(\frac{\beta}{\pi}\right)$, for angles $\alpha$ and $\beta$?

Given two angles $\alpha$ and $\beta$, is there a nice geometric way to construct $\pi \left(\frac{\alpha}{\pi}\right)\cdot\left(\frac{\beta}{\pi}\right)$? It does not necessarily need to be with ...
10
votes
1answer
606 views

What is known in general about the liquid transfer problem?

In several puzzle books, I have seen the following kind of a problem: there are several containers that can hold up to certain amounts of liquid (these liquids are assumed to be infinitely divisible). ...
2
votes
0answers
123 views

Finding an optimal strategy for a combinatorial sequential game

We are given a set $\{p_1, p_2, \ldots, p_n\}$ of players and a set of $\{\ell_1, \ell_2, \ldots, \ell_n\}$ of locations, where $n\in\mathbb{N}$. Each location can be either free or occupied, and each ...
4
votes
0answers
157 views

Social media for a mathematics related idea buckets

Are there any good social media platforms that can recommended for communicating ideas related to mathematics? The reason for asking is that I am in the situation that, albeit having studied math, I ...
4
votes
2answers
176 views

Is there more than one pseudo-Catalan solid?

This question was asked on MSE a year ago. Motivation for this question can be found in other MSE questions here, here or here. Convex solids can have all sorts of symmetries: the platonic solids are ...
12
votes
4answers
2k views

Throwing a fair die until most recent roll is smaller than previous one

I roll a fair die with $n>1$ sides until the most recent roll is smaller than the previous one. Let $E_n$ be the expected number of rolls. Do we have $\lim_{n\to\infty} E_n < \infty$? If not, ...
4
votes
1answer
235 views

Asymptotics for $\prod(1-\frac{1}{p})$ over all primes $p\leq x$ with $p \equiv 3 \bmod 4$

Let us define the following functions: \begin{equation*} \small A(x)=\prod_{\substack{p\leq x\\ p\equiv 3 \bmod 4}} \Big(1-\frac{1}{p}\Big), \mbox{ } \mbox{ } B(x)=\prod_{\substack{p\leq x\\ p\...
10
votes
2answers
180 views

Maximal in-degree in directed voting graph

Real-life motivation. Our team has $n$ members. For the next in-team presentation session, everyone had 1 talk prepared that he or she would be able to present. Now everyone could cast $1$ vote about ...
9
votes
0answers
624 views

A New York Times tiles-based graph theory question

The New York Times has a daily puzzle named Tiles that works as follows. Start with $m$ squares (in the official version, this is 30, in a 6x5 grid), and a set of $p>4$ possible patterns (typically ...
4
votes
1answer
222 views

Map $f:\mathbb{N}\to\mathbb{N}$ such that every 2-set is a neighbor exactly once

Is there a map $f:\mathbb{N}\to\mathbb{N}$ such that for all $a,b\in\mathbb{N}$ with $a\neq b$ there is exactly one $n\in\mathbb{N}$ such that $\{a,b\} = \{f(n),f(n+1)\}$?
3
votes
0answers
361 views

While solving the 1988 IMO problem 6, I have questions about new solutions without using Vieta Jumping [closed]

I think most of you may know the well-known problem: "Let $x$ and $y$ be positive integers such that $xy + 1$ divides $x^{2} + y^{2}$. Show that $\frac {x^{2} + y^{2}}{xy + 1}$ is the perfect ...
6
votes
3answers
2k views

“Gray code” for building teams

Motivation. In a team of $n$ people, we had the task to build subteams of a fixed size $k<n$ such that every day, $1$ person of the subteam is replaced by another person in the team, but not in the ...
1
vote
1answer
224 views

Brinksmanship: how to achieve the best outcome by a single statement [closed]

This game is taken from Schelling's Game Theory: How to Make Decisions by R.V. Dodge, in which contenders practice brinksmanship to their own advantages. It goes as follows: Anderson, Barnes, and ...
5
votes
1answer
286 views

Game on a square grid

Not research level, comments are welcome. Consider the following game: The board is the vertices of an $n$ by $n$ square grid. Two players take moves in turns. A move is picking two vertices and ...
8
votes
1answer
686 views

Recreational mathematical papers [closed]

Sometimes it is nice to get a less technical paper on mathematics to read and learn something different for a change. These papers often make us discover some new curiosity, to think about the process ...
2
votes
1answer
80 views

How to turn a shuffled deck of card into bits

Suppose I fairly shuffle a deck of 52 playing cards, and I want to generate some bits. You could look at each pair of cards, see which is higher or lower, and output either a 0 or 1. That's 26 ...
27
votes
1answer
834 views

The lion and the zebras

The lion plays a deadly game against a group of $N$ zebras that takes place in the steppe (= an infinite plane). The lion starts in the origin with coordinates $(0,0)$, while the $N$ zebras may ...
1
vote
1answer
154 views

Bike lock graph

Motivation. I have a bike lock with 4 dials, and I was wondering whether I can reach any combination by always turning a fixed number $k$, say $k=2$, of the dials, by $1$ position, instead of just ...
2
votes
3answers
331 views

Generations until fixation: A nontrivial generalization of a dice convergence problem

In spite of its "recreational" aspect, this question appears to me to be research-level and (I hope) clearly formulated and tagged. Edit 4/4/20: You can find a related question with the ...
2
votes
1answer
144 views

Increasing the “shuffling distance” by iterating a permutation $\varphi: \omega \to \omega$

Motivation. I was wondering about the following when playing a card-shuffling game with my elder son. If $\varphi: \omega \to \omega$ is a bijection, we define the shuffling distance of $\varphi$ by $...
1
vote
1answer
95 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 ...
7
votes
0answers
462 views

Borderline Collatz-like problems

The usual Collatz map is $C:n \mapsto n/2$ if $n$ even, $(3n+1)/2$ if $n$ odd. Let $f^{\circ (r+1)}:=f \circ f^{\circ r}$. We suspect that for every fixed $n>0$, the sequence $C^{\circ r}(n)$ ...
1
vote
1answer
178 views

Looking for an efficient way of maximising 'pair scores' for subset of 30 selected from 50 to 10 000 objects

Context: I have a tiling program that uses a directed breadth first search algorithm. It is 'directed' by what I call 'pair scoring'. There are $N$ polyforms (pieces) used in the tiling. I have an $N\...
4
votes
2answers
681 views

Coin flipping game

Motivation. My elder son played the following game. He had a bunch of coins, all with heads up, arranged in a circle. He flipped one coin, so that it showed tails, then he moved $1$ position clockwise,...
4
votes
1answer
150 views

Iterated product of digits

It is well-known that the interated sum-of-digits function equally distributes the numbers from $1$ to $10^k-1$ to the digits $1,\ldots,9$. And this holds true for any base $b$. For example, see the ...
11
votes
2answers
424 views

Algebraic properties of graph of chess pieces

For the purpose of this question, a chess piece is the King, Queen, Rook, Bishop or Knight of the game of chess. To a chess piece is attached a graph which represents the legal moves it can make on an ...
5
votes
0answers
181 views

Is Domineering on any finite approximation of the Sierpinski Carpet always a second-player win?

The game of Domineering can be played on any board consisting of some subset of $\mathbb{Z} \times \mathbb{Z}$. In particular, consider the boards $K_n$ generated by iterating the following inductive ...
1
vote
0answers
140 views

Perfect squares of the form $ab^n+c$ and a Diophantine equation

The motivation for this question comes from the following problem from an international Team selection test of 2007 from Chile: Problem: Let $p$ be a prime number. Find all pairs of positive ...
0
votes
2answers
105 views

Majority-driven manipulations of integer vectors

Motivation. Recently I was watching two people play a game that involved arranging sticks in a number of heaps and moving them around in certain allowed ways that I think I was able to infer from ...
11
votes
3answers
1k views

How can I simplify this sum any further?

Recently I was playing around with some numbers and I stumbled across the following formal power series: $$\sum_{k=0}^\infty\frac{x^{ak}}{(ak)!}\biggl(\sum_{l=0}^k\binom{ak}{al}\biggr)$$ I was able ...
11
votes
0answers
410 views

Does Chu and Hough's solution to the mixing time of the 15-puzzle carry over to the Rubik's cube?

In his 1988 book Group Representations in Probability and Statistics , Diaconis considers mixing times of the 15-puzzle. He states: Here is a simplified version: Consider the blank as a $16$th block,...
5
votes
2answers
427 views

Magic $\mathbb{Z}\times\mathbb{Z}$-square

Is there an injective map $j:\mathbb{Z}\times \mathbb{Z} \to \mathbb{Z}$ satisfying: For every $z\in \mathbb{Z}$ we have $$\lim_{N\to \infty}\sum_{k=-N}^Nj(k,z) = 0 = \lim_{N\to \infty}\sum_{k=-N}^Nj(...
1
vote
0answers
380 views

Magical $\mathbb{Z}\times\mathbb{Z}$-square [duplicate]

Now duplicate of Magic $\mathbb{Z}\times\mathbb{Z}$-square where it has an answer. Is there an injective map $j:\mathbb{Z}\times \mathbb{Z} \to \mathbb{Z}$ satisfying: For every $z\in \mathbb{Z}$ we ...
7
votes
1answer
280 views

What is the form of the $(v_0,v_1)$-pizza curve?

Assume that there are two (competing) pizza houses situated at the points $0$ and $1$ on the complex plane. These pizza houses can deliver pizza to points of the plane with the largest velocities $v_0$...
6
votes
1answer
227 views

Guessing the number of other $1$'s in a binary sequence

I have posed the following question on math.stackexchange.com but have not received an answer. So I would like to seek experts' opinion here. Consider the set of all binary sequence of length $n+1$, $...
-4
votes
1answer
289 views

Numbers representable as in the famous IMO question number 6 (1988)

The famous problem number 6 of the 1988 International Mathematical Olympiad is about showing that if $a,b$ are non-negative integers such that $\frac{a^2+b^2}{ab+1}$ is an integer, then it is a square ...
4
votes
0answers
231 views

Numbers with a square sum arrangement

Informal version. For which $n>1$ can the numbers $1,\ldots, n^2$ be arranged in a square form such that the sums of the numbers in the little squares (consisting of $4$ numbers) are all equal? ...
5
votes
1answer
169 views

Complete folds and one cut

The fold-and-cut theorem states that any shape with straight sides can be cut by a single complete straight cut if the paper is the folded flat in the right way. Here is an example from an answer on ...
7
votes
1answer
292 views

Knight's tour problem

It is known that on an infinite board, if all squares of the form $(ki,kj)$ are removed, $k$ even, $i,j\in\mathbf{Z}$, then there is no knight's tour due to unbalanced black and white squares. My ...
8
votes
0answers
117 views

Pursuit-evasion with many slow pursuers

Question: Suppose that intelligent pursuers with speed $v<1$ are randomly scattered on the plane with area density $1/r$  ($r>0$ is distance from the origin). If you start at the origin ...

1
2 3 4 5