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Prime Pairs satisfy Quintic = Cubic (Posted on 2024-02-17) Difficulty: 3 of 5
Given that each of p and q is a prime number:

Determine all possible pairs (p,q) that satisfy this equation:

        p(p4+p2+10q) = q(q2+3)

  Submitted by K Sengupta    
Rating: 5.0000 (1 votes)
Solution: (Hide)
If p=q, then we have lhs > rhs. Accordingly, it follows that p ≠ q.

If p>3, then p| q^2+3, and hence -3 is a quadratic residue in (mod p) and consequently:
p ≡ 1(mod 3).

Then, looking at modulo 3, we get:
p(p^4+p^2+10q) ≡ q+2(mod 3)
while, q(q^2+3) ≡ q(mod 3)

By Fermat's Little Theorem, or by direct check, this leads to a contradiction.

Checking the values p=2,3, we find that:
the only solution is (p,q) = (2,5).

Comments: ( You must be logged in to post comments.)
  Subject Author Date
No SubjectK Sengupta2024-02-22 23:33:03
Woah Daniel Adams2024-02-22 15:18:40
re(2): Analytic solution with computer verificationLarry2024-02-18 09:23:00
p=2xdog2024-02-17 21:50:59
re: Analytic solution with computer verificationBrian Smith2024-02-17 19:04:00
Some ThoughtsAnalytic solution with computer verificationLarry2024-02-17 18:34:10
Some Thoughtsprobable solutionCharlie2024-02-17 15:52:16
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