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

12 votes
Accepted

Why are the only numbers $m$ for which $n^{m+1}\equiv n \bmod m$ also the only numbers such ...

Let $m > 2$ be an integer such that $S_m(m) = \sum_{n=1}^{m-1} n^m\equiv 1 \bmod{m}$. (Taking away $m^m$ does not harm the question, of course). Then $S_m(m)$ has the following expression in terms of …
Chris Wuthrich's user avatar
5 votes
Accepted

Reciprocity law for number fields defined by torsion points of modular elliptic curves

The first question is answered in Serre's [Propriétés galoisiennes des points d'ordre fini des courbes elliptiques, Invent. Math. 15:4 (1972) 259--331], on page 304, section 5.2, exactly for this cur …
Chris Wuthrich's user avatar
1 vote

Consider a sequence $a_i=p \mod a_{i-1}$, where $p$ is a prime number, how to estimate the s...

This is a long comment rather than an answer. Let $p$ be a prime. Consider the map $f(a)$ which assigns to $0<a<p$ the remainder of $p$ modulo $a$. The questions asks when the sequence $a$, $f(a)$, $ …
Chris Wuthrich's user avatar
8 votes
Accepted

Cohomology of elliptic curves

More generally let k be a local field of residual characteristic $\ell$ and $E/k$ an elliptic curve with good reduction. Then for any prime $p\neq\ell$, there is a perfect duality between $E(k)/p^n$ a …
Chris Wuthrich's user avatar
2 votes

For an elliptic curve $E/\mathbb{Q}$ can the cohomology group $H^1(\text{Gal}(\mathbb{Q}(E[p...

$\newcommand{\FF}{\mathbb{F}}\DeclareMathOperator{\SL}{SL}$ OK, let me try. Write $M=E[p]$. If the order of $G$ is coprime to $p$, then $H^1(G,M)=0$. Assume that $p$ divides the order of $G$. Now by …
Chris Wuthrich's user avatar
6 votes
Accepted

Determining $\mu$-invariant of elliptic curves over $\mathbb{Q}$

At what prime ? Well, let $p$ be an odd prime at which $E$ has good ordinary reduction. There are two ways: Use sage or magma to compute the analytic $p$-adic L-function via modular symbols. In sage …
Chris Wuthrich's user avatar
6 votes
Accepted

Isogeny classes and reduction types of elliptic curves at primes of bad reduction

Let $E$ be an elliptic curve over a $p$-adic field $k$. Let $\varphi: E \to E'$ be an isogeny defined over $k$. Write minimal Weierstrass equations with integer coefficients for both curves. Write $\ …
Chris Wuthrich's user avatar
4 votes
Accepted

Iwasawa invariants

Both $\mu$ and $\lambda$ are about the $\Lambda$-torsion part of $M$. Neither of both invariants is visible in either $M/pM$ or $M[p]$ over $\Omega=\mathbb{F}_p[\![T]\!]$. The $\Lambda$-rank of $M$ …
Chris Wuthrich's user avatar
3 votes

Pontryagin dual

Let $X$ be the Pontryagin dual of $M$. Then the dual of $M[p]$ is $X/pX$. Now it is easy to see from the decomposition theorem for modules over the Iwasawa algebra $\Lambda = \mathbb{Z}_p[\![T]\!]$ th …
Chris Wuthrich's user avatar
2 votes

Do isogenies with rational kernels tend to be surjective?

Here is a rather long comment in which I try to justify why I think that the majority will have a surjective map on the Mordell-Weil group. I would not want to guess what the % is. Let $E$ be an elli …
Chris Wuthrich's user avatar
13 votes
Accepted

Is (n,m)=(18,7) the only positive solution to n^2 + n + 1 = m^3 ?

sage: E = EllipticCurve([0,0,1,0,-1]) sage: E Elliptic Curve defined by y^2 + y = x^3 - 1 over Rational Field sage: E.integral_points() [(1 : 0 : 1), (7 : 18 : 1)]
Chris Wuthrich's user avatar
13 votes

Torsion subgroups in families of twists of elliptic curves

Let me expand my comment above. While we believe that we expect this very very frequently, it is not always the case. As I commented, we have $$ E_d(\mathbb{Q})[n]\oplus E(\mathbb{Q})[n] = E(\mathbb …
Chris Wuthrich's user avatar
1 vote
Accepted

Inverse Problem for Iwasawa Modules

I guess $X_{\infty}$ stands for the Galois group of the maximal abelian unramified $p$-extension of $K_{\infty}$, in other words the projective limit of the $p$-primary part of the class groups. Since …
Chris Wuthrich's user avatar
2 votes
Accepted

Euler characteristics in the rank one case

Let $E$ be an elliptic curve over a number field $F$ and $p$ a prime such that $E$ has good ordinary reduction at all places above $p$. Suppose we know that the dual $X$ of the usual Selmer group over …
Chris Wuthrich's user avatar
3 votes
Accepted

Wiman's method for bounding the rank of an elliptic curve

I have not read all the details of the article, but most of what I see is just descent by the isogeny $[2]$. The map is the Kummer map $$E(\mathbb{Q})\to \mathbb{Q}^{\times}/\square \times \mathbb{Q}^ …
Chris Wuthrich's user avatar

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