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Diophantine equations are polynomial equations $F=0$, or systems of polynomial equations $F_1=\ldots=F_k=0$, where $F,F_1,\ldots,F_k$ are polynomials in either $\mathbb{Z}[X_1,\ldots,X_n]$ of $\mathbb{Q}[X_1,\ldots,X_n]$ of which it is asked to find solutions over $\mathbb{Z}$ or $\mathbb{Q}$. Topics: Pell equations, quadratic forms, elliptic curves, abelian varieties, hyperelliptic curves, Thue equations, normic forms, K3 surfaces ...

4 votes

Algorithm for computing rational points if the rank of Jacobian is 0

Here is a sketch of a method that could be able to do what you want. (I won't call it an algorithm, since I cannot prove that it will always work.) I will write $X$ for the curve and $J$ for its Jacob …
Michael Stoll's user avatar
6 votes
Accepted

Algorithm for computing rational points if the rank of Jacobian is 0

There is an algorithm due to Bjorn Poonen (Computing torsion points on curves, Experiment. Math. 10 (2001), no.3, 449–465) that, given a (not necessarily rational) base-point $P_0$ on the curve, finds …
Michael Stoll's user avatar
7 votes

Rational points on genus 3 curves defined by short equations

I have looked a bit at the first equation. It has (at least) seven rational points (as a projective curve). The differences of these points generate a free abelian group of rank three in the Mordell-W …
Michael Stoll's user avatar
11 votes
Accepted

Existence of rational points on generalized Fermat quintics

Both curves have no rational points. Curves of this shape map to genus 2 curves of the form $y^2 = a x^5 + b$ (one can make $a = 1$ if one likes), by quotienting out by the group of automorphisms gene …
Michael Stoll's user avatar
35 votes
Accepted

Is equation $xy(x+y)=7z^2+1$ solvable in integers?

There is no solution. It is clear that at least one of $x$ and $y$ is positive and that neither is divisible by 7. We can assume that $a := x > 0$. The equation implies that there are integers $X$, $Y …
Michael Stoll's user avatar
10 votes
Accepted

On the Diophantine equation $x^{5} + y^5 = z^p$

To the best of my knowledge, this is open for general $p$. As mentioned by Alapan Das, Bjorn Poonen has solved the case $p = 2$ and also $p = 3$ [B. Poonen, Some diophantine equations of the form $x^n …
Michael Stoll's user avatar
7 votes

Are all partial consecutive harmonic subsums distinct?

Here is a partial result: If we fix $a < b$, then there are at most finitely many $(c,d)$ such that $H(a,b) = H(c,d)$. First note that, from the asymptotics, $d-c$ must get large with $c$. Now consi …
Michael Stoll's user avatar
17 votes
Accepted

Find all rational solutions of $x^2(x+1)(x^2+1)(x-1)=2(y+1)(y-1)$

This is no complete answer yet, but may get expanded to one in due course. First we search for points on the curve, which is isomorphic to $$C \colon y^2 = 2(x^6 - x^2 + 2);$$ this produces points wi …
Michael Stoll's user avatar
12 votes

What is the rank of the Mordell equation $y^2 = x^3 - 2$?

You could have a look at this paper: M. Stoll, On the arithmetic of the curves $y^2 = x^\ell + A$, II; J. Number Theory 93, 183-206 (2002). Corollary 2.1 says that for $A = -2$, one gets a rank bo …
Michael Stoll's user avatar
17 votes

Are there any rational solutions to this octic equation?

Considering your equation as a quadratic equation in $m$, it is equivalent to $$y^2 = 4 x^9 + 1$$ (with $y = 2xm + 1$). A solution will in particular give a rational point on the elliptic curve $E \co …
Michael Stoll's user avatar
14 votes
Accepted

Imprimitive solutions to $x^2+y^3=z^7$

You can find the solutions for any given $z$ by looking for the integral points on the elliptic curve $$x^2 = (-y)^3 + z^7$$ (which would usually be written $y^2 = x^3 + z^7$). The curve is isomorphic …
Michael Stoll's user avatar
4 votes
Accepted

On elliptic curves, $\sqrt{x^2-101y^2} ,\sqrt{x^2+101y^2}$, and their ilk

The possible $m_k$, when assumed to be squarefree, must be divisors of the resultant of $x^2 + a$ and $x^2 + b$, which is $(a-b)^2$; so $m_k \mid a-b$. (Note that bot factors must be in the same squar …
Michael Stoll's user avatar
132 votes
Accepted

Estimating the size of solutions of a diophantine equation

This problem turned out to be much more interesting than I originally thought. Let me give my solution, which seems to be slightly different from (but essentially the same as) the solution in the pape …
Michael Stoll's user avatar
10 votes
Accepted

Why are some solutions of these diophantine equations off the usual patterns?

I take this from my comments above and add something. The question is about rational points on the surface $S$ given by $$ \Delta(a,b,c) := (ab+bc+ca)^3 - 27(abc)^2 = z^2 $$ in the weighted projectiv …
Michael Stoll's user avatar
9 votes

rational numbers and triangular numbers

There should always be solutions unless $kn$ is a square. The equation is equivalent to $$k (2a+1)^2 - n (2b+1)^2 = k - n.$$ Let $(x_0, y_0)$ be the fundamental solution of the Pell equation $x^2 - 4 …
Michael Stoll's user avatar

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