# Questions tagged [primes]

Primes or prime numbers are numbers which are divisible only by themselves and one, starting with 2, 3, 5, 7, 11.... They are commonly used in encryption and hashing algorithms.

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### Computation of primality

I believe I have achieved computation of primality! That is, the computation of prime numbers. The code I am about to post will give you every prime there is, in order, starting with 2. Can we call ...
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### Calculate and make a database of prime numbers

I recently created a program for finding a prime number. It's working great and doing it very fast but I was wondering if you can help me make it calculate the prime numbers faster. ...
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### Finding Wilson Primes

A Wilson prime is a prime number p such that p² divides (p−1)!+1. The first three Wilson Primes are 5, 13 and 563 and the fourth is larger than $2×10^{13}$. I was curious as to how much memory/...
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### Accumulate the charAt(*) for each n

This is a helper function, along with three others. It should be called as a .filter(); to return only prime numbers. It is for one of the exercises at FreeCodeCamp....
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### Finding the first 10 million primes

I'm trying to find the first 100 million primes and am trying to find the most efficient way to do it. Can I get some advice on how I could improve this? ...
1k views

### Sum of maximum primes as another prime below a million

This is a project Euler Problem #50. Here is my solution with the problem. ...
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### A faster way to compute largest prime factor (Again, but a lot better)

I came up with this code after implementing the feedback given by @200_success. The previous one (A faster way to compute the largest prime factor) tested my patience, but still failed to give the ...
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### Finding primes from random integers

I was hoping I could get some help making my code more efficient. I'm a math major taking an Intro to Programming class, and I was asked to write a C program that generates: A text file named ...
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### Produce all multiples of a set of primes up to a certain limit

I have some Python code that generates all possible multiples and combinations of a given set of primes up to a certain limit. The code runs and does exactly what I intend it to do, now I am trying to ...
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### A non-static Sieve of Eratosthenes class, version 1

Over the years I’ve seen many C# sieves and despite their varying internals all that I have seen invariably are a static method that returns a List<int>, ...
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### Review my prime factorization function. Is it complete?

This is a function designed to return all the prime factors of a given number, in sorted order from least to greatest, in a list. It relies on another function that checks if a given number is prime. ...
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### Naïve Prime Factorization in Clojure Pt. 2

After my last review request, I decided to try and make a "tree" visualization, and thought that I could benefit from making find-prime-factors lazily produce prime ...
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### Prime number generation - SPOJ

This is a program to generate prime numbers for a given range. The sieve of Eratosthenes algorithm was implemented, but still the SPOJ says time limit exceeded. Where can some optimizations be made? ...
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### Project Euler #50 Consecutive prime sum

I'm having trouble optimising the project euler #50 exercise, it runs for around 30-35 seconds, which is terrible performance. The prime 41, can be written as the sum of six consecutive primes: ...
536 views

### Speeding up Mersenne prime generator

I am writing a program to calculate Mersenne primes. This code works, but it is so slow: ...
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### Prime conjecture [closed]

I am trying to solve this SPOJ question. ...
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### Problem in calculating prime numbers in python [closed]

I'm a noob in programming. I was asked to code a program that can calculate prime numbers. So i coded as provided below. But it prints all the Odd Numbers instead of Prime Numbers. I think the Value ...
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### Euler Project #3 Largest prime factor timeout

I have been recently trying my hands on Euler's Project through HackerRank and got stuck with project #3 where you have to find the Largest Prime Factor. Question: The prime factors of 13195 are 5, 7,...
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### Printing all the factors as well as the prime factors of a given number using Python 2.7.x

Okay here is my maiden attempt at programming using Python 2.7. I need help or feedback on this code: How do I know about the processing cycles this program consumes? How do I implement this idea ...
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### Project Euler # 3 in Haskell: largest prime factor of some number

The program works, but is extremely slow. Project Euler problem 3 Problem: What is the largest prime factor of the number 600851475143? ...
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### Finding prime numbers performance

I am writing an app that finds prime numbers within a specified range. Currently i am updating almost every part of the app and i have also changed the way i find prime numbers. The problem is that ...
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### Scala implicit conversion to add methods to Int

I started learning Scala, and like most functional languages, things get messy pretty quickly for a beginner. Here I have built a wrapper class for Ints so that I ...
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### Calculating the prime numbers between two integers

I've wrote this code to calculate the prime numbers between two integers n and m, and I want to optimise it. ...
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### Getting prime numbers between a range

I have the following code to get the prime numbers between a range of numbers. Is this the best and fastest method? ...
213 views

### Largest prime factor function

I have written a function which finds the largest prime factor of some number. This function works but the problem is that it is too slow. For instance, when I enter 600851475143 as a parameter, the ...
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### Decomposing a number into primes

I have written the following code to decompose a number into primes. The problem is that it takes so much time and I have no idea why. ...
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### For pairs of elements, count the ones whose XOR value is a sum of two primes [closed]

An array is given with 'n' Values ( n <= 10^5 ) ; we have to calculate xor of each pair of elements and count those pairs whose xor can be written as sum of two prime numbers with the same parity(...
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### prime function in a for loop using Math operations [closed]

guys I saw a function(the function is just below) that check wether a number is prime and return a value but I don't understand the operations made in the code. Can someone explain me mathematically?...
511 views

### Largest prime factor of a given number

I'm solving Problem 3 in Project Euler: The prime factors of 13195 are 5, 7, 13 and 29. What is the largest prime factor of the number 600851475143? Most answers I found made use of array to ...
295 views

### Prime Number Generator

The purpose of this program is to run an infinite prime generator that won't stop unless I tell the console to stop. This is not a sieve of Eratosthenes; it stores prime numbers in an array and ...
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### Motorola 6809 Prime finder

I'm trying to make a small program which takes a number (form 1 to 1000) and shows the primes between 2 and that number. Right now I have a quite functioning program (except a couple of bugs), but the ...
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### Project Euler problem # 3 is this the most efficient approach in Python or can I do better?

The problem statement: The prime factors of 13195 are 5, 7, 13 and 29. What is the largest prime factor of the number 600851475143 ? This code takes 9 seconds!, is there a better way? ...
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### Testing primality

This method accepts an int parameter and verifies if the parameter is a prime number by trial division. It returns a Boolean value of true if it is prime or ...
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### Closest Prime Number via Letters [closed]

I'd like this code to be optimized and factorized, along with, perhaps, re-making it so it's more readable via introducing better functions and minimizing the lines needed for it to be human-readable (...
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### Printing a prime normalized sequence

The program below generates a prime normalised sequence. So, what happens is this: It asks you to provide a number within a range. Program then calculates a factor which is inverse of product of all ...