Timeline for Is there any positive integer sequence $c_{n+1}=\frac{c_n(c_n+n+d)}n$?
Current License: CC BY-SA 3.0
7 events
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Dec 10, 2018 at 15:26 | comment | added | Sam Hopkins | @WillSawin: phrased this way, the transformation sort of looks like those found in the theory of cluster algebras, so maybe if there is a positive answer to the question it could be found via the "Laurent phenomenon." | |
Dec 10, 2018 at 1:59 | comment | added | AxiomaticSystem | If we ignore the division by n, a necessary condition for the integrality of the original sequence is for the modified $c_{p+1}$ to divide $p$ for all primes $p$. Might it be possible to show that given any $c_1$ and $d$, that there must exist a prime $p$ such that this is not the case? | |
Sep 27, 2017 at 19:11 | history | edited | Ilya Bogdanov | CC BY-SA 3.0 |
`increasing' added
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Sep 27, 2017 at 17:05 | comment | added | Sam Hopkins | A note that you may want to allow the sequence to start at $c_k$ for some $k>1$ because otherwise the motivating example is not really of this form. | |
Sep 27, 2017 at 15:57 | history | edited | Max Alekseyev | CC BY-SA 3.0 |
spelling:)
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Sep 27, 2017 at 15:48 | comment | added | Will Sawin | We can express this as a time-invariant dynamical system by adding an additional variable $n$, i.e. $(x,y) \to (x+1, y(y+x+d)/x)$. For each prime $p$, this naturally gives an algebraic dynamical system on $\mathbb Q_p \times \mathbb Z_p$. One wants to know if there is a $d$ such that all these systems stay inside $\mathbb Z_p \times \mathbb Z_p$ forever. Maybe techniques of $p$-adic algebraic dynamics would be helpful here? | |
Sep 27, 2017 at 15:35 | history | asked | Ilya Bogdanov | CC BY-SA 3.0 |