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

7 votes

Coin flipping game

To complete the proof of Dieter Kadlka: For $n=2^m$, we are looking for $a\neq b< n$ such that $$ b^2+b=a^2+a+l 2^{m+1} $$ for some $l\in \mathbb{N}$ and then $$l 2^{m+1} = (b-a)(b+a+1)$$ Because $b-a …
RaphaelB4's user avatar
  • 4,361
18 votes

Sets of unit fractions with sum $\leq 1$

The bound proposed by Lucia is correct. I add some detail and I stress that It is an application of "large deviation" theorem which is very very standard. Set the following independent Bernoulli rand …
RaphaelB4's user avatar
  • 4,361
4 votes
Accepted

How many roots of polynomial in $\mathbb Z[x]$ and $\mathbb Q[x]$ are integers on average?

$$\mathbb{E}[\text{#|roots of P|}]=\mathbb{E}(\sum_{k\in \mathbb{Z}}1_{k \text{ is a root of P}})=\sum_{k\in\mathbb{Z}}\mathbb{P}(P(k)=0)$$ For $k=0$, $\mathbb{P}(P(0)=0)=\frac{1}{(2B+1)}$. For $k\ne …
RaphaelB4's user avatar
  • 4,361