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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 …
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 …
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:
$$ \ …
31
votes
Is there any theory why (for Bitcoin) the discrete logarithm problem is so hard to solve?
Yes. I'll talk about why elliptic curve discrete log is harder than ordinary discrete log.
Suppose we have $g, h$ and want to find $n$ such that $g^n = h$.
The usual methods for solving the discrete …
8
votes
Accepted
Any results towards the irrationality of the sum of reciprocals of perfect numbers?
As Stanley Yao Xiao commented, a definite answer to this question would be equivalent to solving an open problem. If we assume two reasonable conjectures, however, then the sum $\sigma$ of the recipro …
14
votes
Accepted
Is there a set of positive integers of density 1 which contains no infinite arithmetic progr...
Another construction is to let $n \notin V$ if and only if $n$ begins with at least $\sqrt{\log{n}}$ consecutive '9's when written in decimal. This satisfies the stronger property that there is no non …
4
votes
Accepted
What was the first elementary proof that $\pi(x)=o(x)$?
Leonhard Euler knew that the infinite product:
$$ \prod_{p \textrm{ prime}} \left(1 - \frac{1}{p} \right)^{-1} = \sum_{n=1}^{\infty} \frac{1}{n} $$
is divergent (and used this to prove the infinitud …
6
votes
Accepted
Yet another question on sums of the reciprocals of the primes
It's well known that the sum of the reciprocals of the primes below $n$ tends to $\log \log n + M$, where $M$ is a small constant (the Meissel-Mertens constant). That is to say:
$$ \sum\limits_{\smal …
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 $ …
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 …
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 …
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 …
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 …
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 $ …