Questions tagged [math]

The challenge involves mathematics in some central way. Also consider using more specific tags, listed in the tag wiki info.

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391
votes
156answers
269k 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. ...
326
votes
55answers
108k 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 ...
192
votes
61answers
30k 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 ! ...
171
votes
99answers
39k 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 ...
163
votes
5answers
17k 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 ...
130
votes
11answers
13k views

(-a) × (-a) = a × a

We all know that \$(-a) \times (-a) = a \times 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 ...
106
votes
369answers
18k views

One OEIS after another

As of 13/03/2018 16:45 UTC, the winner is answer #345, by Khuldraeseth na'Barya. This means the contest is officially over, but feel free to continue posting answers, just so long as they follow the ...
103
votes
12answers
9k 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 ...
100
votes
30answers
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 ...
99
votes
38answers
19k 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 ...
90
votes
98answers
20k 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 ...
90
votes
14answers
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 ...
81
votes
176answers
9k 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 ...
81
votes
6answers
37k 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 (...
75
votes
114answers
11k 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 ...
74
votes
175answers
15k 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 ...
73
votes
15answers
14k 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 ...
69
votes
25answers
9k 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 ...
65
votes
10answers
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 ...
63
votes
15answers
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....
60
votes
42answers
13k 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 ...
58
votes
36answers
8k 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 ...
57
votes
10answers
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 <...
56
votes
33answers
6k views

Superstitious hotel elevator

Description Here's a very superstitious hotel elevator in Shanghai:                 It avoids the number 13, because ...
55
votes
9answers
10k 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 ...
55
votes
22answers
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 ...
54
votes
33answers
8k 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 ...
54
votes
75answers
8k 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): \$1^3 + 5^3 + 3^3 = 153\$ \$1634\$: \$1^...
53
votes
18answers
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 ...
53
votes
43answers
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 \$\text{lcm}\$\$(A, B)\$ ...
52
votes
3answers
6k 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 ...
52
votes
9answers
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 ...
51
votes
47answers
8k views

Coprimes up to N

Given a number n >= 2, output all the positive integers less than n where gcd(n, k) == 1 (...
51
votes
57answers
6k views

Multiplicative persistence

Multiplicative Persistence Multiply all the digits in a number Repeat until you have a single digit left As explained by Numberphile: Numberphile "What's special about 277777788888899?" Numberphile ...
51
votes
43answers
14k 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 ...
51
votes
33answers
7k views

Conway's Monster

This challenge is in honor of mathematician John Conway who passed away April 11, 2020 due to COVID-19. He was famous for coming up with the Game of Life cellular automaton and many other mathematical ...
51
votes
37answers
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 ...
51
votes
12answers
5k 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. ...
51
votes
11answers
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 ...
50
votes
66answers
11k views

Divide a number by 3 without using *, /, +, -, % operators [closed]

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 ...
50
votes
47answers
4k views

Count sums of two squares

Given a non-negative number n, output the number of ways to express n as the sum of two squares of integers ...
50
votes
13answers
5k views

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

Consider the positive integer powers of five in decimal. Here are the first 25, right aligned: ...
49
votes
31answers
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, ...
49
votes
13answers
12k 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 ...
48
votes
79answers
10k 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 positive ...
48
votes
73answers
6k views

It's Hip to be Square

Challenge So, um, it seems that, while we have plenty of challenges that work with square numbers or numbers of other shapes, we don't have one that simply asks: Given an integer ...
48
votes
45answers
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 ...
48
votes
26answers
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 ...
48
votes
48answers
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 ...
48
votes
32answers
2k views

Divisor skyline

For any positive integer \$k\$, let \$d(k)\$ denote the number of divisors of \$k\$. For example, \$d(6)\$ is \$4\$, because \$6\$ has \$4\$ divisors (namely \$1, 2, 3, 6\$). Given a positive integer \...

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