Find all prime numbers $ p,q$ less than 2005 and such that $ q|p^2 + 4$, $ p|q^2 + 4$.
Problem
Source: IZO 1 Junior Problem 6
Tags: number theory, relatively prime, number theory unsolved
17.12.2008 03:05
24.06.2009 06:41
The QuattoMaster 6000 wrote:
But how can that be? We say that $ a\le b$. So, $ (a + b)(a - b) \le 4$ is obvious.
24.06.2009 10:12
@Stephen: He means $ a\geq b$. It seems to be a typo.
24.06.2009 13:55
pluricomplex wrote: @Stephen: He means $ a\geq b$. It seems to be a typo. Then how can $ (a, b)=(1, 2)$?
24.06.2009 14:04
http://www.mathlinks.ro/viewtopic.php?p=1353597#1353597 essentially the same problem, but a bit more complicated.
24.06.2009 23:43
Stephen wrote: Then how can $ (a, b) = (1, 2)$? Sorry, I meant $ (a, b) = (2,1)$ and $ a\ge b$.
02.12.2016 23:29
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02.12.2016 23:49
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03.12.2016 16:54
guys please help me i want to understand this part but i can't.PLEASE HELP ME!!!!!! " We now consider the Pell's Equation $ 2m^2 - n^2 = 1$. We can compute the primes $ q$'s that work for the the Pell's Equation under $ 2005$ (they are solutions to the recurrence $ a_{n + 1} = 6a_n - a_{n - 1}$ with $ a_1 = 1$ and $ a_2 = 5$), which are $ 5$ and $ 29$. "
03.12.2016 17:07
See this for a detailed explanation on Pell's equation.
03.12.2016 21:06
fattypiggy123 wrote: See this for a detailed explanation on Pell's equation. Thanks very much
11.12.2016 16:04
i have one question as you found that k equals to 6,can't you apply Vieta jumping after it? I mean that can't you solve the equation $ p^2 - 6pq + (q^2 + 4) = 0$ by Vieta jumping and also when solving that by Vieta,you will find that there is no need to have p,q are less than 2005
21.04.2020 19:59
Anar24 wrote: i have one question as you found that k equals to 6,can't you apply Vieta jumping after it? I mean that can't you solve the equation $ p^2 - 6pq + (q^2 + 4) = 0$ by Vieta jumping and also when solving that by Vieta,you will find that there is no need to have p,q are less than 2005 Actually you can. Just need to revers the step of vieta jumping I mean first consider all pairs that with one jump they reach the root solution $(1,1)$ then those who reach $(2,2)$ in one jump and so on. One can observe that every pair reaches to one of these root answers after some jumps so continuing this processes will give us all solutions. But obviously this is possible only if we have some bound on the solution pairs.
06.12.2021 19:46
pell equation