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

3 votes

Do finite places of a number field also correspond to embeddings?

Just to tack something on about your final question: There exists a rather concrete "yes" answer to your last question in the form of Arakelov theory. One defines an Arakelov divisor as a finite for …
Cam McLeman's user avatar
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5 votes

Fermat over Number Fields

Kolyvagin's "On the First Case of the Fermat Theorem for Cyclotomic Fields" is worth mentioning here. The main point of this paper is that while various case-by-case eliminations (e.g., Kummer's reg …
Cam McLeman's user avatar
  • 8,467
10 votes
Accepted

Explicitly describable maximal unramified extension of a number field

No, I'm pretty sure not. In general, the theory is much more developed for the maximal pro-p-quotient of the groups you're asking about, and even in this more explored setting, not a single explicit …
Cam McLeman's user avatar
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15 votes
Accepted

Unramified extensions of number fields

Two things: 1) Yes, certainly. By class field theory and the finiteness of the class group, the maximal abelian unramified extension of any number field is of finite degree. Thus any infinite un …
Cam McLeman's user avatar
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21 votes

Is there a ring of integers except for Z, such that every extension of it is ramified?

Yes, there are many such fields. (Edit: Let me put up here that "many" is still finite, and only in the hundreds if my list below represents most of the known examples. Note that "state-of-the-art" …
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4 votes

Calculus on rationals

Yes, you get some interesting dynamics out. The derivative with all $\alpha_p=1$ goes by the name "the arithmetic derivative," and there are a few references around (Ufnarovski's being the most compl …
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16 votes

number fields with no unramified extensions?

The question itself is certainly still open. Mostly as an exercise for myself, I'll coalesce my comments above into an answer, and add in some details about where various pieces of the philosophy com …
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32 votes
Accepted

Can an algebraic number on the unit circle have a conjugate with absolute value different fr...

Yes. Take $$ \alpha=\sqrt{2-\sqrt{2}}+i\sqrt{\sqrt{2}-1}. $$ Neither of the conjugates $$ \sqrt{2+\sqrt{2}}\pm \sqrt{\sqrt{2}+1} $$ have absolute value 1. It is impossible, however, if $\mathbb{Q} …
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7 votes
Accepted

Totally real number fields with bounded regulators

I believe the question is: "Does there exist a constant $A$ such that there exists infinitely many totally real number fields with regulator less then $A$?" Ignore this response if that's incorrect. …
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7 votes

Kummer generator for the Ribet extension

Here is an explicit construction$^*$. Since there exists such an unramified $p$-extension, by class field theory the $p$-part of the class group of $\mathbb{Q}(\mu_p)$ is non-trivial. Further, speci …
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10 votes

A coverage question

It is very likely that every (positive) odd number is covered by a sum of this type. As Robin Chapman points out, this is equivalent to asking, for a given odd number $h$, whether there exists an odd …
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13 votes

Does $\pi_1(Spec(\mathbb{Z}[1/p]))$ depend on p?

To add on to Pete's answer, let me comment that the differences are even more pronounced if we look at the maximal pro-$p$ quotient $\pi_1(\operatorname{Spec}(\mathbb{Z}\left[\frac{1}{p_1p_2\cdots p_r …
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2 votes

relations between class numbers of quadratic extensions

The short answer to your question is basically no, there's essentially no connection between the prime powers $q^i$ dividing $h_p$ and $h_{-p}$. It's true that there's a general relationship betwee …
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11 votes
Accepted

sums of rational squares

This result is pretty shy of needing the full Hasse-Minkowski Theorem. Indeed, since Fermat already knew which integers were a sum of two integer squares, it would suffice for him to show that those …
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15 votes
Accepted

How divisible is the average integer?

Hopefully I've read all your notation correctly. If so, by playing (very) fast and loose with heuristics, I think your friend is right that the answer is 0. Your function $Log(n)$ is the additive fu …
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