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

4 votes

how do we prove that a sum of two periods is still a period?

For a given $n \in \mathbb{N}$, consider the algebraic function: $$ f_n : \mathbb{R}^{n+2} \rightarrow \mathbb{C} $$ $$ f_n(x,y,z_1,\dots,z_n) = x + iy $$ We're going to define a 'simple period' to be …
Adam P. Goucher's user avatar
4 votes

Automorphisms of Lubotzky–Phillips–Sarnak graphs

The automorphism group is strictly larger than $G$. Note that the automorphism group is a semidirect product of $G$ with the stabiliser of a single vertex, so it suffices to show that the group of aut …
Adam P. Goucher's user avatar
5 votes
Accepted

Is it a known property of positive integers $n> 2 $ that one must have $n < \mathrm{rad}(n(n...

Suppose we have such an $n$ where $P(n)$ is false. Now define $(a, b, c) := (1, n(n-2), (n-1)^2)$ and observe that these three numbers are pairwise coprime and satisfy $a + b = c$. Then we have: $$ \ …
Adam P. Goucher's user avatar
31 votes

Is there any theory why (for Bitcoin) the discrete logarithm problem is so hard to solve?

Yes. I'll talk about why elliptic curve discrete log is harder than ordinary discrete log. Suppose we have $g, h$ and want to find $n$ such that $g^n = h$. The usual methods for solving the discrete …
Adam P. Goucher's user avatar
8 votes
Accepted

Any results towards the irrationality of the sum of reciprocals of perfect numbers?

As Stanley Yao Xiao commented, a definite answer to this question would be equivalent to solving an open problem. If we assume two reasonable conjectures, however, then the sum $\sigma$ of the recipro …
Adam P. Goucher's user avatar
14 votes
Accepted

Is there a set of positive integers of density 1 which contains no infinite arithmetic progr...

Another construction is to let $n \notin V$ if and only if $n$ begins with at least $\sqrt{\log{n}}$ consecutive '9's when written in decimal. This satisfies the stronger property that there is no non …
Adam P. Goucher's user avatar
4 votes
Accepted

What was the first elementary proof that $\pi(x)=o(x)$?

Leonhard Euler knew that the infinite product: $$ \prod_{p \textrm{ prime}} \left(1 - \frac{1}{p} \right)^{-1} = \sum_{n=1}^{\infty} \frac{1}{n} $$ is divergent (and used this to prove the infinitud …
Adam P. Goucher's user avatar
6 votes
Accepted

Yet another question on sums of the reciprocals of the primes

It's well known that the sum of the reciprocals of the primes below $n$ tends to $\log \log n + M$, where $M$ is a small constant (the Meissel-Mertens constant). That is to say: $$ \sum\limits_{\smal …
José Hdz. Stgo.'s user avatar
7 votes
2 answers
287 views

Elements of absolute value 1 in cyclotomic extension of dyadic rationals

Let $\zeta$ be a primitive $2^k$th root of unity, and consider the ring $ \mathbb{Z}[\zeta, \frac{1}{2}] \subset \mathbb{C}$. Are there any elements of absolute value 1 other than the powers of $\zeta …
15 votes
Accepted

Find all integer solutions to $y^2=x^5+4.$ Is it true that the only solutions are $(x, y) = ...

Yes, these are the only examples. Either $x$ is zero (your $(0, \pm 2)$ example) or not; assume the latter. Rewrite your equation as $(y - 2)(y + 2) = x^5$, and appeal to unique factorisation. Then $ …
Adam P. Goucher's user avatar
10 votes
Accepted

Finding the largest number which cannot be the sum of the labels of the Petersen graph

I can prove that all sufficiently large integers are representable. Firstly, observe that there is a unique way, up to isomorphism, to choose three edges $p, q, r$ of the Petersen graph such that the …
Adam P. Goucher's user avatar
9 votes

A labelling of the vertices of the Petersen graph with integers

It is possible to exploit the symmetries of the Petersen graph, together with the rearrangement inequality, to reduce the size of a brute-force search from $15!$ to $129729600$ (a $10080$-fold improve …
Adam P. Goucher's user avatar
2 votes

Are there non-commutative models of arithmetic which have a prime number structure?

Commutativity is not necessary for the notion of primes. For instance, consider the Hurwitz integers, namely quaternions whose components are either all integers or all half-integers: $$ H = \{ a + b …
Adam P. Goucher's user avatar
6 votes

Which even numbers are known to be both prime gaps and the sum of 2 primes?

Definition: A weak prime gap is an integer which occurs infinitely often as the difference between two (not necessarily adjacent) primes. We'll show that the set of weak prime gaps has positive densi …
Adam P. Goucher's user avatar
9 votes
Accepted

"Fractally self-similar" numbers

Before you can formulate your question precisely, you need a better notion of distance between two pictures of a set $S \subset \mathbb{C}$ (where in this case, $S$ is the union of Ford circles). If $ …
Adam P. Goucher's user avatar

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