speed up prime number generating?

Question

This program generates prime numbers . It works well but I want to speed it up as it takes quite a while for generating the all the prime numbers

#!/usr/bin/python

#intgr = int(raw_input ("Please enter your number: "))
intgr = 50000

for i in range (2, intgr+1):
    j = 2
    while j<i:
        if (i%j) == 0:
            break
        j += 1
    if j == i:
        #print "prime", i
        pass #print "prime", i
print "done"

it takes about 15 seconds to run right now i would like to decrease that time.

First off, I'm assuming python2, since the print statement at the end is only valid in python2, I'd use xrange() instead of range(). — Nick Vitha, Apr 04 '19 at 20:32
You should look up algorithms created to generate prime numbers, for example the sieve of eratosthenes — DeepSpace, Apr 04 '19 at 20:32
Your condition should be `while j <= sqrt(i)` (clearly I'm not familiar with python syntax). The `if` after that, too. — Wai Ha Lee, Apr 04 '19 at 20:36

Code-Apprentice · Answer 1 · 2019-04-04T20:33:11.810

-2

Generating prime numbers is inherently slow. The algorithm you implemented is known as Trial Division and is one of the slowest ways to generate primes. There are other algorithms which are much faster, for example the Sieve of Eratosthenes. I suggest you do some more research about better algorithms.

edited Apr 04 '19 at 20:33

answered Apr 04 '19 at 20:31

Code-Apprentice

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According to wikipedia, it's not the fastest, but the simplest. I'm not really sure this answer needs to be more than a comment, btw. – Blorgbeard Apr 04 '19 at 20:33
4

Shouldn't this be a comment? – DeepSpace Apr 04 '19 at 20:33

speed up prime number generating?

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