Comments on: Project Euler Problem 3 http://basildoncoder.com/blog/2008/04/07/project-euler-problem-3/ Incoherent and disjointed opinionated drivel from somewhere near London Sat, 22 Nov 2008 16:17:55 +0000 http://wordpress.org/?v=2.3.1 By: -jn- http://basildoncoder.com/blog/2008/04/07/project-euler-problem-3/#comment-913 -jn- Sun, 20 Apr 2008 00:09:18 +0000 http://basildoncoder.com/blog/2008/04/07/project-euler-problem-3/#comment-913 Interesting! I learned a bit more Python by reading your post. With respect to "only generate primes up to the square root of N", no fudge-factor is needed. Simply keep track of the running quotient. After dividing 15 by 3 to get a quotient of 5, and verifying that 4 is > √15, you know that 5 is prime. It can't have two factors greater than √15 else it woud be > 15 itself. It can't have a factor less than √15, because all of those factors have already been eliminated. Thanks for keeping it going! Interesting! I learned a bit more Python by reading your post.

With respect to “only generate primes up to the square root of N”, no fudge-factor is needed. Simply keep track of the running quotient. After dividing 15 by 3 to get a quotient of 5, and verifying that 4 is > √15, you know that 5 is prime.

It can’t have two factors greater than √15 else it woud be > 15 itself. It can’t have a factor less than √15, because all of those factors have already been eliminated.

Thanks for keeping it going!

]]> By: Prime time programming « Sliding up the banister http://basildoncoder.com/blog/2008/04/07/project-euler-problem-3/#comment-912 Prime time programming « Sliding up the banister Sat, 19 Apr 2008 23:32:29 +0000 http://basildoncoder.com/blog/2008/04/07/project-euler-problem-3/#comment-912 [...] noticed that Basildon Coder had a post on this same problem. I held off reading it until after working through my own approach, [...] […] noticed that Basildon Coder had a post on this same problem. I held off reading it until after working through my own approach, […]

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