All about flooble | fun stuff | Get a free chatterbox | Free JavaScript | Avatars    
perplexus dot info

Home > Just Math
Getting Primed With Subtraction And Addition (Posted on 2007-12-26) Difficulty: 2 of 5
Determine all possible primes p such that each of p-8, p-4, p+8 and p+12 are also primes.

See The Solution Submitted by K Sengupta    
No Rating

Comments: ( Back to comment list | You must be logged in to post comments.)
Solution Solution | Comment 3 of 5 |
All primes greater than 3 are of 6k+1 or 6k-1
Let p-8 > 11 => p>19

Case(i): Let p=6k-1
then p-8 = 6k-9 = 3*(2k-3)
So, p-8 is not prime

Case(ii): Let p=6k+1
then p-4 = 6k-3 = 3*(2k-1)
So, p-4 is not prime in this case
The only value that satisfies these conditions is p=11.

  Posted by Praneeth on 2007-12-27 00:49:41
Please log in:
Remember me:
Sign up! | Forgot password

Search body:
Forums (0)
Newest Problems
Random Problem
FAQ | About This Site
Site Statistics
New Comments (2)
Unsolved Problems
Top Rated Problems
This month's top
Most Commented On

Copyright © 2002 - 2021 by Animus Pactum Consulting. All rights reserved. Privacy Information