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

Home > Just Math
Prime pair (Posted on 2023-11-17) Difficulty: 3 of 5
Find all pairs (p,q) of prime numbers such that

p(p2-p-1)=q(2q+3)

No Solution Yet Submitted by Danish Ahmed Khan    
No Rating

Comments: ( Back to comment list | You must be logged in to post comments.)
Possible Solution Comment 3 of 3 |
Let p(p2-p-1)=q(2q+3) with p,q, prime

p does not divide q, so p must divide (2q+3), say a times.
(2q+3)=a*p,p=(2q+3)/a

Substituting:

((2q+3)/a)(((2q+3)/a)^2-((2q+3)/a)-1)=q(2q+3)

Less of a mess than it looks, since (2q+3)^2 = a(a^2q+a+2q+3),

Evaluate RHS for small values of a: 
0,
(3q+4), 
2(6q+5)
3(11q+6)
4(18q+7)
5(27q+8)
...

(2q+3)^2=5(27q+8), with q=31 is the sole positive integer value for q (so a is also prime).
But then p=(2q+3)/a= (62+3)/5=13 must be the sole positive integer value for p

So the answer is {p,q}={13,31}

  Posted by broll on 2023-11-17 22:47:59
Please log in:
Login:
Password:
Remember me:
Sign up! | Forgot password


Search:
Search body:
Forums (0)
Newest Problems
Random Problem
FAQ | About This Site
Site Statistics
New Comments (15)
Unsolved Problems
Top Rated Problems
This month's top
Most Commented On

Chatterbox:
Copyright © 2002 - 2024 by Animus Pactum Consulting. All rights reserved. Privacy Information