# Questions tagged [math]

The challenge involves mathematics. Also consider using more specific tags: [number] [number-theory] [arithmetic] [combinatorics] [graph-theory] [geometry] [abstract-algebra].

1,284 questions
235k views

### Write a program that makes 2 + 2 = 5 [closed]

Write a program that seemingly adds the numbers 2 and 2 and outputs 5. This is an underhanded contest. Your program cannot output any errors. Watch out for memory holes! Input is optional. ...
103k views

### Tweetable Mathematical Art [closed]

Integer math can generate amazing patterns when laid out over a grid. Even the most basic functions can yield stunningly elaborate designs! Your challenge Write 3 Tweetable (meaning 140 characters ...
28k views

### Mathematics is fact. Programming is not

In mathematics an exclamation mark ! often means factorial and it comes after the argument. In programming an exclamation mark !...
37k views

### Programming Languages Through The Years

In this challenge, users will take turns completeing three fairly simple coding tasks in programming languages that are allowed to be progressively older. The first answer must use a programming ...
13k views

### Hyperprogramming: N+N, N×N, N^N all in one

Write a program that takes in a number N from 1 to 9 inclusive. In its native form your program should output N+N. E.g. output 2 if N is ...
11k views

### (-a) × (-a) = a × a

We all know that (-a) × (-a) = a × a (hopefully), but can you prove it? Your task is to prove this fact using the ring axioms. What are the ring axioms? The ring axioms are a list of rules that two ...
16k views

### One OEIS after another

As of 13/03/2018 16:45 UTC, the winner is answer #345, by Scrooble. This means the contest is officially over, but feel free to continue posting answers, just so long as they follow the rules. As ...
6k views

### Does the code terminate?

This is a code golf challenge I thought of with a mathematical bent. The challenge is to write the shortest code possible such that it is an open question whether or not the code terminates. An ...
6k views

### The Colors in Our Stars

Write a program that takes in a string or text file whose first line has the form width height and each subsequent line has the form ...
7k views

### Proving that a Russian cryptographic standard is too structured

The aim of this challenge is to find an impossibly short implementation of the following function p, in the langage of your choosing. Here is C code implementing it ...
18k views

### When does (x == x+2)? [closed]

The challenge: Define x in such a way that the expression (x == x+2) would evaluate to true. I tagged the question with C, but ...
15k views

### Mandelbrot image in every language

I always used a Mandelbrot image as the 'graphical' version of Hello World in any graphical application I got my hands on. Now it's your guys' turn. Language must be capable of graphical output or ...
31k views

### Hard code golf: Regex for divisibility by 7

Matthias Goergens has a 25,604-character (down from the original 63,993-character) regex to match numbers divisible by 7, but that includes a lot of fluff: redundant parentheses, distribution (...
7k views

### Output the sign

Given a number N, output the sign of N: If N is positive, output 1 If N is negative, output -1 If N is 0, output 0 N will be an integer within the representable range of integers in your chosen ...
8k views

### Collatz Conjecture (OEIS A006577)

This is the Collatz Conjecture (OEIS A006577): Start with an integer n > 1. Repeat the following steps: If n is even, divide it by 2. If n is odd, multiply it by 3 and add 1. It is proven that ...
17k views

### 9 Hole Challenge [closed]

The 9 Hole Challenge 9 code golfing challenges of varying difficulty. Penalties for using the same language more than once. The question will be updated with pars, hole champions and trophy winners....
9k views

### Calculate the number of primes up to n

π(n) is the number of primes less than or equal to n. Input: a natural number, n. Output: π(n). Scoring: This is a fastest-code challenge. Score will be the sum of times for the score cases. I ...
8k views

### Yo boy, must it sum

Every positive integer can be expressed as the sum of at most three palindromic positive integers in any base b≥5.   Cilleruelo et al., 2017 A positive integer is palindromic in a given base if ...
5k views

### How lit is this mountain? 🔥

A mountain is defined to be a set of line segments whose first point has coordinates (0,a) where a > 0, and whose last point ...
12k views

### Find the Smoothest Number

Your challenge is to find the smoothest number over a given range. In other words, find the number whose greatest prime factor is the smallest. A smooth number is one whose largest prime factor is ...
13k views

### Sum of all integers from 1 to n

I'm honestly surprised that this hasn't been done already. If you can find an existing thread, by all means mark this as a duplicate or let me know. Input Your input is in the form of any positive ...
10k views

### Little Chandler is sad. Draw him a cloud to cheer him up

Little Chandler is sad. Draw him a cloud to cheer him up. Note: Drawing a cloud won't actually cheer him up. A circle can be defined as a 3-tuple (x,y,r) where <...
5k views

### Superstitious hotel elevator

Description Here's a very superstitious hotel elevator in Shanghai:                 It avoids the number 13, because ...
7k views

### Test a number for narcissism

A Narcissistic Number is a number which is the sum of its own digits, each raised to the power of the number of digits. For example, take 153 (3 digits): 13 + 53 + 33 = 1 + 125 + 27 = 153 1634: ...
8k views

### Program that adds all natural numbers and yields -1/12 [closed]

As you might know there is a mathematical fun-fact that if you add all natural numbers you end up with... -1/12 (see Wikipedia here). Of course this is very strange result and can not be obtained by ...
3k views

### Dennis numbers 2.0

PPCG user and elected mod, @Dennis just became the second ever user to earn over 100k rep! This is a totally original idea, that I did not get from anybody else, but let's make a challenge based off ...
5k views

### Quiche Lorraine [closed]

Since it was Pi day recently, I have noticed a number of challenges that ask you to calculate pi. Of course, a quiche lorraine is not quite a pie (you can claim a Bonus Score¹ of +1 if you guessed ...
5k views

### Print the N-bonacci sequence

This isn't very widely known, but what we call the Fibonacci sequence, AKA 1, 1, 2, 3, 5, 8, 13, 21, 34... is actually called the Duonacci sequence. This is ...
4k views

### Help me with differential calculus!

I love programming and know every language, but I suck at math. Unfortunately, my school requires that computers students must take a year of calculus. There's a test next week, and I don't know any ...
4k views

### 5, 2, 16, 3580, What comes next?

Consider the positive integer powers of five in decimal. Here are the first 25, right aligned: ...
3k views

### Bringing a pair of integers to equality

This was inspired by a math problem I saw somewhere on the internet but do not remember where (UPDATE: The original problem was found on the math riddles subreddit with a proof provided that it is ...
5k views

### Coprimes up to N

Given a number n >= 2, output all the positive integers less than n where gcd(n, k) == 1 (...
4k views

### How many steps does it take from n to 1 by subtracting the greatest divisor?

Inspired by this question over at Mathematics. The Problem Let n be a natural number ≥ 2. Take the biggest divisor of ...
3k views

### Illustrate the Least Common Multiple

Given two positive integers, A and B, illustrate their least common multiple by outputting two lines of dashes (-) with length LCM(A, B) after replacing every Ath ...
4k views

### Alex is sometimes right

This challenge is to lift the spirits of our mod Alex A., who is usually wrong. Suppose you have a friend named Alex who needs help with basic logic and math, specifically mathematical equivalence. ...
11k views

### “Disprove” Fermat's Last Theorem [closed]

Write a program, in the language of your choice, that appears to successfully find a counterexample to Fermat's Last Theorem. That is, find integers a, b, c > 0 and n > 2 such that an + bn = cn. Of ...
7k views

### Calculate a square and a square root!

You must make a polyglot that outputs the square of the input in one language and the square root of the input in another. The shortest answer in bytes wins! You must have a precision of at least 3 ...
5k views

### Detect heat waves

Background The Royal Netherlands Meteorological Institute defines a heat wave* as a series of at least 5 consecutive days of ≥25°C weather (“summery weather”), such that at least 3 of ...
5k views

### Knight on the Rim is Grim

Introduction Aron Nimzowitsch was a leading chess master and a influential chess writer. In his book 'My System', the first chapter deals about the importance of the center and why you should ...
3k views

### Too Fast, Too Fourier: FFT Code Golf

Implement the Fast Fourier Transform in the fewest possible characters. Rules: Shortest solution wins It can be assumed that the input is a 1D array whose length is a power of two. You may use the ...
5k views

### The Snail in the Well

Background There's a common riddle that goes something like this: A snail is at the bottom of a 30 foot well. Every day the snail is able to climb up 3 feet. At night when they sleep, they slide ...
9k views

### Is my triangle right?

Given a, b, c the length of the three sides of a triangle, say if the triangle is right-angled (i.e. has one angle equal to 90 degrees) or not. Input Three ...
6k views

### Golf a transcendental number

Definitions An algebraic number is a number that is a zero of a non-zero polynomial with integer coefficients. For example, the square root of 2 is algebraic, ...
10k views

### Divide a number by 3 without using *, /, +, -, % operators

Quoting this question on SO (Spoiler alert!): This question has been asked in an Oracle interview. How would you divide a number by 3 without using *, /, +, -, %, operators? The number ...
8k views

### Draw/plot a heart graph

Your challenge is to draw/plot one of the hearts below. The size must be at least 50x50 pixels (vector graphics is OK). You may choose which of the hearts you want to draw/plot. Axes, grid lines etc. ...
4k views

### Greater than less than greater than something fishy

Given a length N string of less-than and greater-than signs (<, >), insert the integers 0 through N at the start and end ...
5k views

### Count without 3

Background When I was in elementary school, we used to play a game in math class that goes as follows. All kids sit in a big circle and take turns counting, starting from 1. However, the following ...
7k views

### Golf a number bigger than TREE(3)

The function TREE(k) gives the length of the longest sequence of trees T1, T2, ... where each vertex is labelled with one of k colours, the tree Ti has at most i vertices, and no tree is a minor of ...