# 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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### 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. ...
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### 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 ...
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### 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 ! ...
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### 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 ...
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### 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 ...
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### (-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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 (...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### Factorial in haiku!

Task Create a program that calculates the factorial of a number using no built-in factorial functions. Easy? The catch is that you must write your entire program (including testing it) in haiku form. ...
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### 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....
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### The vanilla factorial challenge

Task Given a non-negative integer $n$, evaluate the factorial $n!$. The factorial is defined as follows: $$n!=\begin{cases}1 & n=0\\n\times(n-1)!&n>0\end{cases}$$ Rules All default I/...
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### Moving modest minimum

Inspired by a question over at Stack Overflow. The title here is entirely my fault. The challenge Given a list of positive integers containing at least two entries, replace each number by the ...
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### 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 ...
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### Is this number a factorial?

The Task Given a natural number as input, your task is to output a truthy or falsey value based on whether the input is a factorial of any natural number. You can assume that the input number will ...
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### 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 ...
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