Register    Login    Search    Rss Feeds

Forums Home » Ask An Instructor » GMAT Math » GMAT Prep Math


 Page 1 of 1 [ 2 posts ] 



  Print view Print view Previous topic Previous topic | Next topic Next topic
 

Factorials and Prime Numbers

Author Message
manochsa
 Post subject: Factorials and Prime Numbers
 Post Posted: Mon Oct 26, 2009 1:16 pm 
Offline
Course Students


Posts: 8
Is there a way to determine whether n! +/- 1 will be a prime number?

For example if n = 4:
4! + 1 = 25 --> not a prime number
4! -1 = 23 --> a prime number

Thanks,

Sanjay
Top 
Ben Ku
 Post subject: Re: Factorials and Prime Numbers
 Post Posted: Thu Nov 19, 2009 4:17 am 
Offline
ManhattanGMAT Staff


Posts: 823
To determine whether a number is prime is hard enough; determining whether one more than a factorial is prime is very challenging. I'm sure you can find some proof for this somewhere, but it is not needed for the GMAT.

If you need more clarification, please give an example of a problem where this idea is needed might be needed so we can provide a helpful response.

_________________
Ben Ku
Instructor
ManhattanGMAT
Top 
Display posts from previous:  Sort by  
 
 Page 1 of 1 [ 2 posts ] 





Who is online

Users browsing this forum: No registered users and 1 guest

 
 

 
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to: