A prime number is a number that is only divisible by 1 and itself.

learn more… | top users | synonyms

0
votes
0answers
31 views

very simple prime program [on hold]

I keep getting the error floating point exception (core dumped). For this simple prime test I made. I am very new to C++ so I'm having trouble tracking down the bug. #include <iostream> using ...
21
votes
8answers
973 views

Fond Memories of Past Primes

Consider a prime number p, written in base 10. The memory of p is defined as the number of distinct primes strictly less than p that are contained as substrings of p. Challenge Given a non-negative ...
37
votes
12answers
4k views

A naturally occurring prime generator

There are quite a large number of prime generating functions. Pretty much all of them are constructed and are based on the sieve of Eratosthenes, the Möbius function or the Wilson's theorem and are ...
-7
votes
7answers
179 views

Puzzle: Factor these 256-bit semiprimes [closed]

Challenge Write a program to factor this set of 10 numbers: 15683499351193564659087946928346254200387478295674004601169717908835380854917 ...
18
votes
12answers
1k views

Sum of smallest prime factors

SF(n) is a function which computes the smallest prime factor for a given number n. We'll call T(N) the sum of every SF(n) with 2 <= n <= N. T(1) = 0 (the sum is over 0 summands) T(2) = 2 (2 ...
16
votes
2answers
3k views

Prime Nerd Sniping Pattern

Longest day of the year - here's something to waste the extra time... Overview Note this is not a popularity contest and not a graphical output challenge - you are only required to output a string ...
7
votes
7answers
639 views

Recursive Prime Factorization

Your job is to take the prime factors of a number taken from input (omitting any exponents equal to 1) then take the prime factors of all of the exponents, and so on, until no composite numbers ...
7
votes
3answers
228 views

Number of ways to sum [1..n] with [n+1..2n] such that each sum is prime

Let n > 0. Let X = [1..n] and Y = [n+1 .. 2n]. Define a(n) as the number of permutations p of Y such that every element of X + p(Y) is prime. For example: n = 2 X = [1,2] Y = [3,4] p0(Y) = [3,4] ...
7
votes
10answers
676 views

List Sophie Germain primes

The Question A Sophie Germain prime is a prime p such that 2p+1 is prime as well. For example, 11 is a Sophie Germain prime because 23 is prime as well. Write the shortest program to calculate Sophie ...
20
votes
2answers
488 views

Factoring a 64-bit integer

Write a GOLF assembly program that reads an integer from stdin (followed by a trailing newline), and outputs its prime factors seperated by newlines, followed by a trailing newline on stdout. The ...
17
votes
1answer
339 views

Prime polynomials

Given a polynomial, determine whether it's prime. A polynomial is ax^n + bx^(n-1) + ... + dx^3 + ex^2 + fx + g, where each term is a constant number (the coefficient) multiplied by a nonnegative ...
8
votes
3answers
654 views

Self-shortening Prime Tester

Let's get right in to it. Your challenge is to make a program that does these things depending on its input: If the input is a number, output "Prime" if the number is a prime number and "Not prime" ...
8
votes
2answers
649 views

Finding Programs in the Primes

Let's assign the numbers 0 through 94 to the 95 printable ASCII characters: !"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~ Space is 0, ! is 1, and ...
11
votes
7answers
1k views

Finding prime numbers without using “prime characters”

Your task, if you choose to accept it, is to write a program/function that accepts an integer N as input. The program/function should output/return a list of the first N prime numbers. But here's the ...
7
votes
3answers
918 views

Recognize Twin Primes by Crashing

Background Story Bob was handed the following assignment for his programming class. Please note: this is not the actual challenge. Homework assignment 11: Twin primes Input: an integer n ...
14
votes
4answers
582 views

Factorize it! …badly

A curious kid uses a program which can factorize a number or an expression into the following form: p1^e1 * p2^e2 * ... * pn^en. Exponents equal to 1 are omitted e.g. 360 = 2^3 * 3^2 * 5 The kid ...
9
votes
8answers
545 views

Pair-golfing Twin primes and the Collatz sequence

This is a new kind of challenge inspired by the Recover the mutated source code problem. You should write two programs or functions both in the same language. The first one should solve Task #1 and ...
7
votes
24answers
1k views

Cops and Robbers bowling (Robbers)

Robbers' Thread In this challenge, your goal is to crack some code written by the Cops (their code is here) by modifying it. You have cracked their code if: Your modified code has a maximum ...
15
votes
26answers
1k views

Cops and Robbers bowling (Cops)

Cops' Thread In this challenge, your goal is to write a function that accepts a integer N, and that function will return the first N primes. However, you must do this in the most characters ...
8
votes
5answers
1k views

All primes from 0 to 1000

Is it possible to make this C code smaller? It prints out all primes from 0 to 1000. C, 89 chars int i,p,c;for(i=2;i<1e3;i++){c=0;for(p=2;p<i;p++)if(i%p==0)c++;if(c==0)printf("%u\n",i);}
21
votes
6answers
2k views

Find the largest fragile prime

Consider the function Remove(n, startIndex, count) that removes count digits from the number n starting from the digit at position startIndex. Examples: Remove(1234, 1, 1) = 234 Remove(123456, 2, 3) ...
3
votes
3answers
231 views

Preprocessing primality

The challenge: Given an integer N, 1 < N < 2³¹, write code that uses the C preprocessor to determine whether N is prime, and produces a "Hello world" program if N is prime, or an error ...
7
votes
4answers
655 views

Build a Primitive Root Diffuser

Introduction When a room has bare, parallel walls, it can create unpleasant repeating acoustic reflections (echoes). A diffuser is a device mounted on a wall which creates a blocky surface of many ...
5
votes
7answers
689 views

Shortest code to find next prime palindrome

I was trying to find the shortest code possible that given a number n, returns the next prime palindrome number (limited to below 100000). If the number itself is a prime palindrome, the code should ...
12
votes
9answers
700 views

Combinatorial products of unique primes

Statement of problem Given a set of unique, consecutive primes (not necessarily including 2), generate the products of all combinations of first powers of these primes — e.g., no repeats — and also ...
9
votes
4answers
799 views

Anagramming Code

Let's try this again. The object of this contest is to make two pieces of code that are anagrams of each other (the two must contain the same bytes in a different order), and they will do the ...
12
votes
8answers
2k views

These Primes of Mine Are Always Solid Lines

Let's create a N×N grid of spaces and underscores that can be used to visually determine if a number is prime. (N may be any positive integer.) This grid has three simple rules: The nth column ...
39
votes
26answers
8k 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 ...
8
votes
5answers
1k views

Find the craftiest prime

Intro Consider the process of taking some positive integer n in some base b and replacing each digit with its representation in the base of the digit to the right. If the digit to the right is a 0, ...
12
votes
1answer
300 views

Primality Testing in Manufactoria

Background Manufactoria is a game about programming. The player must use a form of two-dimensional programming language to complete tasks. If you've never heard of it, the easiest way to learn is to ...
11
votes
7answers
891 views

is_gaussian_prime(z)?

Task Write a function that accepts two integers a,b that represent the Gaussian integer z = a+ib (complex number). The program must return true or false depending on whether a+ib is a Gaussian prime ...
-1
votes
2answers
284 views

Find prime which is generating longest primes sequence using p(n+1)=(p(n)^2+1)/2

Consider following recurrence relation: p[n + 1] = (p[n]^2 + 1) / 2 If p[1], p[2], ..., p[k] are primes and p[k+1] is not, then k is length of sequence starting with p[1]. For example, if p[1] = 3, ...
30
votes
10answers
4k views

Find the largest prime whose length, sum and product is prime

The number 113 is the first prime whose length 3 is prime, digital sum 5 = 1 + 1 + 3 is prime, and digital product 3 = 1 * 1 * 3 is prime. A prime that has these 3 properties will be called supremely ...
8
votes
1answer
829 views

Palindromic prime

I'm solving task, where: Input: A number as an integer. Output: The closest greater palindromic prime as an integer. I would appreciate hints how to make my solution shorter. Or directions if ...
12
votes
7answers
3k views

Determine if a number is prime without using arithmetic [duplicate]

Write a program which determines if a given number is prime. The catch: No digits or arithmetical operators. This means: No digits from 0 to 9, anywhere in the program, and whatever the meaning No ...
15
votes
28answers
2k views

Calculate prime gaps

Finding primes is a programming rite of passage and very frequently a first serious program someone crates (usually with trial division). But primes alone are already worn out. A next far more ...
10
votes
11answers
804 views

Find the smallest prime from a substring

In 1946 Erdos and Copeland proved that a certain number is a normal number, i.e. the digits in its decimal expansion are uniformly distributed. Users will input a sequence of digits and you will find ...
11
votes
8answers
1k views

Is it a prime? w/o math

Write a program or function in any language that tells if the input is a prime number. The input is a string representing a natural number in base-10. The output is one of the two strings "Prime" or ...
13
votes
24answers
2k views

Goldbach's conjecture

Write a program that prompts the user for an even integer greater than 2. Given Goldbach’s conjecture that every even integer greater than 2 can be expressed as the sum of two primes, print out two ...
4
votes
4answers
152 views

Quine with prime sourcecode character distribution constraints

Your program should take no input, and no network or other connections. Your program should output it's sourcecode. The sourcecode must consist of 3 types of characters: Numeric (0-9), Alpha ...
4
votes
10answers
657 views

Circular primes

Given a number determine if it is a circular prime. A circular prime is a prime where if you rotate the digits you still get prime numbers. 1193 is circular prime because 1931 and 9311 and 3119 are ...
6
votes
5answers
373 views

Enumerate the primes using only unary arithmetic

Write a program which prints the sequence of prime numbers. The shortest solution wins! All numbers must have a unary representation (not just in the output, but throughout the entire program). This ...
4
votes
7answers
563 views

Nth K-Ugly Number

Write the shortest code in any language of your choice to find the Nth K-ugly number. A K-ugly number is a number whose only prime factors are the prime numbers <= K. This K-ugly number is ...
0
votes
0answers
63 views

Fastest way to generate Smarandache–Wellin number [duplicate]

Given a number n find the Smarandache–Wellin number for n. Ex: for n=2 output=23 for n=5 output=235711 Answer it in ruby or python. given constraints are n<=70000
13
votes
19answers
1k views

Give the smallest number that has N divisors

Your function takes a natural number and returns the smallest natural number that has exactly that amount of divisors, including itself. Exemples: f(1) = 1 [1] f(2) = 2 [1, 2] f(3) = 4 [1, 2, 4] ...
16
votes
6answers
1k views

Find largest prime which is still a prime after digit deletion

Over at http://math.stackexchange.com/questions/33094/deleting-any-digit-yields-a-prime-is-there-a-name-for-this the following question is asked. How many primes are there that remain prime after you ...
7
votes
3answers
5k views

Fastest code to find the next prime

The problem is as follows. Input: An integer n Output: The smallest prime bigger than n. The challenge is to give the fastest code possible to do this. I will test the code on values starting at ...
15
votes
2answers
4k views

Fastest semiprime factorization

Write a program to factorize a semi-prime number in the shortest amount of time. For testing purposes, use this: 38!+1 (523022617466601111760007224100074291200000001) It is equal to: ...
3
votes
2answers
401 views

List ALL prime-factorized natural numbers in ANY order

This is a variant of List prime-factorized natural numbers up to N in ascending order, but the solutions can be very different. Write a program that outputs prime factorizations of all natural ...
5
votes
2answers
1k views

List prime-factorized natural numbers up to N in ascending order

For a given n list prime factorization of all natural numbers between 1 and n in ascending order. For example, for n = 10 the output would be: 1: 2: 2^1 3: 3^1 4: 2^2 5: 5^1 6: 2^1 3^1 7: 7^1 8: 2^3 ...