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Prime numbers, diophantine equations, diophantine approximations, analytic or algebraic number theory, arithmetic geometry, Galois theory, transcendental number theory, continued fractions

7 votes

Rational zeros of a polynomial

The polynomial defines a genus 2 curve. Your curve is birational to the genus two curve $C$ given by $y^2=x^5+7x^4+18x^3+24x^2+16x+4$. This curves has two rational Weierstrass points. These points cor …
Remke Kloosterman's user avatar
12 votes

Computing factorials modulo p^N

I believe that the question whether $(p-1)! \bmod p^2$ is computable in polynomial time is still open. The best I am aware of is $O(p^{1/2+\epsilon})$, but I am not a specialist on this issue. The co …
Remke Kloosterman's user avatar
12 votes
Accepted

Counterexample to Proposition of Granville related to abc conjecture

I checked the proof of Granville. The proof only yields the bound $\max \{ \deg(r),\deg(s)\}(\deg(G)-2)\}+1$ which covers your counterexample. To be more detailed: The polynomials $r,s$ yield a morph …
Remke Kloosterman's user avatar
4 votes

Non-coprime solutions to x^n+y^n = z^2

The answer to the question depends on the parity of $n$. Suppose that $n=2k$ is even. Let $(x,y,z)$ be a nonzero solution to your equation, with $y\neq 0$. Then $(x/y,1,z/y^k)$ is also a solution of …
Remke Kloosterman's user avatar
11 votes
Accepted

Mordell-Weil of an elliptic surface after adjoining a nontorsion section: as small as possible?

I do not believe you have equality in general. I sketch a counterexample below, which is a geometric version of the fact that if $E/K$ is an elliptic curves such that the quadratic twist $E^{(d)}/K$ h …
Remke Kloosterman's user avatar
5 votes

Mordell-Weil of an elliptic surface after adjoining a nontorsion section: as small as possible?

I will sketch a counterexample for the modified question. The idea behind the construction is similar to the counterexample for the original question. Only the geometric details of this construction a …
Remke Kloosterman's user avatar
5 votes
Accepted

Selmer of an abelian variety versus that of its dual.

Let $\varphi:A\to A^t$ be a polarization. Then $\varphi$ is an isogeny. In order to study the difference between the Selmer groups of $A$ and of $A^t$ you need to study the torsion subgroups of $A(K)$ …
Remke Kloosterman's user avatar
3 votes

Polarizations of K3 surfaces over finite fields

Let $S$ be a smooth projective surface and $m:=\gcd(\deg \lambda)$ where $\lambda$ runs through the ample cone. Let $m'$ be the gcd of the entries of the intersection matrix of $S$ Then $m$ equals ei …
Remke Kloosterman's user avatar
16 votes

Rank of $x (x^2 - 1) = c (c^2 - 1) y^2 $ over $\mathbb{Q}$ for given rational values of $c$

First you use $c$ as a parameter, i.e., consider your equation as elliptic curve over $\mathbb{Q}(c)$. You can also consider this equation as an equation of an elliptic surface $S$. Now one easily pr …
Remke Kloosterman's user avatar
9 votes

What heuristic evidence is there concerning the unboundedness or boundedness of Mordell-Weil...

I am not aware of much evidence for arbitrary high rank elliptic curves. Silverman in his book (Arithmetic of elliptic curves) gives as evidence the lack of evidence for the opposite statement. I gues …
Remke Kloosterman's user avatar
4 votes

weight 4 eigenforms with rational coefficients---is it reasonable to expect they all come fr...

I am not that sure that your question can be answered positively, but the following is merely speculation, so you should not pin me down on it. The basic idea is that there might be "more" weight 4 fo …
Remke Kloosterman's user avatar
10 votes

Does $(x^2 - 1)(y^2 - 1) = c z^4$ have a rational point, with z non-zero, for any given rati...

If you take the projective closure of your surface in $\mathbb{P}^3$ you find a singular quartic. This quartic has six singular points. Namely the two points found by Daniel and four points of the for …
Remke Kloosterman's user avatar