# Tagged Questions

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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### Unbounded Sieve of Eratosthenes in Swift

I've spent a while teaching myself Swift, and decided to take on the challenge of writing an unbounded Sieve of Eratosthenes to challenge myself. This is actually the first time I've written an ...
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### Finds all the prime numbers up to n using a strange pattern

Here's an odd pattern I found for sieving out composite numbers to find primes. I wrote it myself, originally thinking I made an indexing error, but it turned out to work after removing squares. <...
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### Sieve of Eratosthenes and twin prime finder

I made this program to find primes and twin pairs. I'd like feedback on anything from formatting to content to technique. In short: how would this be different if it was written by an experienced ...
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### The Miller-Rabin Primality Test in Clojure

I am new to clojure and I wanted to test out my skills by taking an existing implementation written in Python and writing it in Clojure. Concerns My main concerns are where I use ...
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### Looking for primes with all-different digits

I recently answered a question on Mathematics Stack Exchange, where I used a small Python program to check the following : For all 6-digit numbers, with all digits being different, choosing the ...
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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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### PrimeFactorize method for int

I have written this PrimeFactorize utility method in C# (using LINQPad) which works fine, but feels like it is a bit slow, I was wondering what might be improved. ...
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### Approaching a C++ library with templates

I previously posted a thread asking for a general review of one of my first projects related to programming (C++ Prime Number Library) and received very good help and new perspectives. After this, I ...
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### TLE on SPOJ for Prime Generator (PRIME1)

The objective is to find all primes between two given numbers. It is specified that the two numbers are $\le$ 1 billion and the difference between the two numbers is ~100,000. We are to repeat the ...
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### Project Euler 3: Largest prime factor

How can I improve my code, make it more efficient, and are there any tips you have? Project Euler 3: The prime factors of 13195 are 5, 7, 13 and 29. What is the largest prime factor of the ...
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### Palindromic prime search using the Sieve of Atkins

I am working on a project that deals with prime numbers and am currently looking for a way to make the function max_palprime() work faster and possibly simpler. ...
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### Snakes on a prime

The challenge is to find and print the largest palindrome prime under 1000. ...
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### C++ Prime Number Library

This prime number library is one of my first programming projects I've done in c++. My goal is to create useful functions that deal with prime numbers in an efficient way.Note: (Most of the functions ...
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### C the sum of primes

The challenge is to calculate the sum of the first 1000 primes. The code applies a sieve thanks to past answer, here, and works but I wonder about the flexibility of this solution. ...
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### Prime number checker in Python 3 - follow-up

I have updated my code from the last time it got reviewed. If anyone has some more suggestions on how I can improve this and/or make it faster it would be appreciated! ...
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### Largest Prime Factor (PE3) using OOP

I want to learn some C# syntax/paradigms (I'm more used to Java), and have been wanting to get a bit better at math as well, so I solved ProjectEuler3: Largest prime factor with the following small ...
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### Prime number calculator in Python 3.4.1

I have only been coding for a short time and I have written these two functions and am looking to optimise them. If anyone could point out things that could be done better it would be much appreciated....
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### Shortest prime number generator we could come up with?

I worked with a friend on the following prime number generator. Our goal was to make it as short and as fast as possible. This is what we came up with: ...
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### Project Euler 10: find the sum of all the primes below two million

This is question #10 from Project Euler: The sum of the primes below 10 is 2 + 3 + 5 + 7 = 17. Find the sum of all the primes below two million. I just started programming and read that a Sieve ...
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### Check if a number is prime

I'm looking for feedback on the following code which checks if a number is prime using Swift 2. ...
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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: ...
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### Finding the prime factors of a positive number

I have an assignment to write on the standard output the prime factors of a positive number displayed in ascending order and separated by '*'. My code works, but I need help reviewing it before I ...
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### Project Euler #49 Prime permutations

Today I solved problem #49 from project euler .net which reads : The arithmetic sequence, 1487, 4817, 8147, in which each of the terms increases by 3330, is unusual in two ways: (i) each of the ...
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### 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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### Calculate the sum of all primes less than 2,000,000 in Swift

This is a Swift program I wrote to calculate the sum of primes below 2 million, but it is tediously slow. I am curious about what makes it so slow. My theory is that copying the filtered array is ...
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### Multiple rusty Sieves of Eratosthenes

To get more familiar with the multi-threading aspects in the Rust language I decided to multi-thread my earlier implementation of The rusty Sieve of Eratosthenes. I have to say that it is probably in ...
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### Symmetry analysis for atom arrangements in a crystal

For a while now I've been meaning to post some of my Haskell code here so that someone can tell me what parts of the language/base library I've been completely overlooking. This is the first thing I'...
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### Number of divisors of a factorial

I was solving the DIVFACT problem from Sphere Online Judge: Given a number, find the total number of divisors of the factorial of the number. Since the answer can be very large, print the answer ...
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### SICP exercise 1.28 - miller-rabin primality test

From SICP Exercise 1.28: One variant of the Fermat test that cannot be fooled is called the Miller-Rabin test (Miller 1976; Rabin 1980). This starts from an alternate form of Fermat’s Little ...
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### Fast nth prime in Python using trial division

I'm trying to speed this code up for larger values of N. Any suggestions? I'd like to stick to this implementation and not move on to something more complex like numpy or sieves. Is there any low ...
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### The rusty Sieve of Eratosthenes

To get familiar with the Rust language I've decided to implement the method of Sieve of Eratosthenes to find primes up to a number N. I have created the following code that both prints the prime ...
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### Printing all prime factors of a number input by the user

I just started teaching myself to code a few days ago using the Euler problems. I finished a variant of problem 3: print the prime factors of a number input by the user. I just want feedback and code ...
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### Primes & Squares

Codeforces #230B Question Whether a number has exactly three factors. (i.e. 1, itself and its square root, thus squares of primes) [Time limit is 2 sec, Memory 256 MB] Input Number of testcases, n ...
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### Counting the number of primes in C and C++11

I found this old piece of code that I wrote while I was learning C a while back: ...
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### Writing a Rustic segmented prime number sieve

I wrote a prime number sieve in Ruby last year as part of a coding challenge, but lately I wanted to port it to Rust. I finally got around to it, but it's still intensely Rubinic. Before I take the ...
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### Prime generator SPOJ problem in Python 3

I am trying to solve an SPOJ problem: print all prime numbers in a given range (as large as $10^9$). I have used the Sieve of Eratosthenes algorithm. But it is still slow when input is in range of \\$...
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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 ...
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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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### A reference source for primes up to 64K (for unit tests)

In order to code the tests for my number theory library (a collection of routines that proved handy for coding challenges) I needed a reference source for primes up to 2^16. I did not want to ...
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### p0-Pollard implementation

I should implement p0-Pollard with C++14 and a good algorithm. How may I improve my code? ...
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### Complete factorization in ><>

Maybe a somewhat odd choice of language, but here is a program in ><> I have tried to optimize the execution time of. (Not golfing). The efficiency is measured in the number of required ...
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### Prime numbers in given range

SPOJ problem PRIME1 (also found on other sites in identical form): Input The input begins with the number t of test cases in a single line (t<=10). In each of the next t lines there are ...
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### Sieve Of Erastothenes using Java

have started learning Java recently and was looking into some easy algorithms. I found the Sieve Of Erastothenes algorithm here I am trying to get better at writing good code for my solutions. Please ...
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### Read numbers until a prime is entered then print non-primes

I'm a beginner at C#. I just want to know what is the C# way to do this by its convention and a better algorithm as well. ...
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### Find prime positioned prime number

This is a question from programming contest. This contest is already over. Now, all the prime numbers are arranged sequentially in ascending order. i.e:- 2, 3, 5,7...and so on. Now, your task is to ...
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### Project Euler #7 10001st prime

I decided to start working on the Euler project exercises. I'm doing fine for now but the seventh problem is running quite slow and I can't think of anything to make it work faster. It takes around ...