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

44 votes
2 answers
7k views

What is known about the sum x^{n^2}/n?

It follows from a general theorem of Honda that the formal group with the logarithm $$ x+x^{2^s}/2+x^{3^s}/3+x^{4^s}/4+\cdots $$ has integer coefficients. I became interested in it because its $p$-typ …
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41 votes

Is the series $\sum_n|\sin n|^n/n$ convergent?

On the OP request, here is the plot of first 10000 partial sums. Following Terry Tao's suggestion, here is the plot of ($n$th partial sum) $+2^{\frac32}/\sqrt{\pi n}$ for $n$ up to one million: …
33 votes

Chebyshev polynomials of the first kind and primality testing

Wow. This deserves a separate answer. As I mentioned in a comment, motivated by the question, in a previous comment, by Igor Rivin whether an efficient primality test can be made if the statement in …
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22 votes
3 answers
1k views

Roots of Bernoulli polynomials - a pattern

Contemplating a question on math.SE, I have stumbled on this: Here, the point labeled $n$ is that root of the $n$th Bernoulli polynomial which has smallest positive imaginary part. Does anyone …
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21 votes

When does doubling the size of a set multiply the number of subsets by an integer?

Just an illustration - for $m$ up to 6000, $r$ up to 120. Quite mysterious looking, I would say. Version 2: in the coordinate system suggested by the answer of Lucia it looks somehow more regular, …
19 votes
2 answers
2k views

Is there an explicit expression for Chebyshev polynomials modulo $x^r-1$?

This is an immediate successor of Chebyshev polynomials of the first kind and primality testing and does not have any other motivation - although original motivation seems to be huge since a positive …
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19 votes
2 answers
775 views

"Fractally self-similar" numbers

This is another question about visualization of Ford circles, the previous one being Confusion with practically implementing rational approximations. Here is an output of zooming into Ford circles at …
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17 votes
0 answers
431 views

Need explicit formula for certain "$q$-numbers" involving gcd's

The question is motivated by yet another possible approach to a combinatorial problem formulated previously in "Special" meanders. I'm not giving details of the connection as I believe the question is …
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16 votes

Prime factorization "demoted" leads to function whose fixed points are primes

NOT AN ANSWER, just an illustration :D ($g$ up to $n=150$) Quite amusing... In case anybody wants to play with this, here is the Mathematica code g[n_] := Dot @@ Transpose[FactorInteger[n]] Graph …
14 votes
Accepted

Structures in the plot of the “squareness” of numbers

At least some part of the features may be explained by plotting $\frac1{r(n)}$, it looks like this: It is more or less clear that the slopes are $\frac1{k^2}$, $k=1,2,3,...$ (So the original plot …
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13 votes

Can one prove the elementary divisor theorem for PIDs by elementary matrix operations?

According to Wikipedia, examples of PIDs with nontrivial $SK_1$ have been first given by Ischebeck in "Hauptidealringe mit nichttrivialer $SK_1$-Gruppe" (Arch. Math. 35 (1980), 138–139) and by Grayson …
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13 votes
2 answers
1k views

A mystery sequence

This question arose from the recent one, roots of a polynomial linked to mock theta function?. Let $$ g(x):=\sum_{k=0}^\infty x^k\prod_{j=1}^{k-1}(1 + x^j)^2\\=1+x+x^2+3 x^3+4 x^4+6 x^5+10 x^6+15 x^7+ …
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13 votes
0 answers
316 views

Work of Atkin on the 26th power of eta

The 26th power of the Dedekind $\eta$ function has been mentioned several times here on MO: A 14th and 26th-power Dedekind eta function identity? What's the status of the following relationship betwee …
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11 votes
1 answer
608 views

Gauss, Jacobi, Kloosterman sums and representation theory in the $\mathbb F_1$-world

This question is inspired by Why are Bessel function and Kloosterman sum similar? - it developed in me desire to understand Kloosterman sums better. There seems to be common knowledge that Gauss, Jac …
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10 votes
1 answer
565 views

Intuitive reasons for the existence of modular parametrizations

Whenever I encounter anything about modular parametrizations, I have a feeling it is something very unnatural: you have some kind of moduli space and all of a sudden it parametrizes an object represen …
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