108,950 reputation
698199
bio website von-eitzen.de/math/tntrep.xml
location Bonn, Germany
age 48
visits member for 1 year, 11 months
seen 5 hours ago

I did study math and had a knack for it, but I am sooo out of that business now ...


Oct
11
comment Prove that $\tau(n) \leq 2\sqrt{n}$
You can replace $\le$ with $<$.
Oct
11
revised Proving that a discrete valuation-like function $w: \mathbb{Z}\backslash\{0\} \rightarrow \mathbb{N}$ is a $p$-adic valuation
added 221 characters in body
Oct
11
answered Proving that a discrete valuation-like function $w: \mathbb{Z}\backslash\{0\} \rightarrow \mathbb{N}$ is a $p$-adic valuation
Oct
11
comment Finite subsets and the Definable Power Set Operation
I don't know the book, but wonder: Does finiteness of $X$ imply that we "know" $n$?
Oct
11
comment What is the symbol $\triangleq$?
+1, except that I don't agree with preferring this symbol ;)
Oct
11
comment Finding the smallest set on which a group acts faithfully
What's trivial are the bounds that $\#G$ divides $\#S!$ and $\#S\le \#G$ or that the answer for cyclic $G$ of order $\prod p^{k_p}$ is $\sum p^{k_p}$, bu tbeyond that things can get messy ...
Oct
11
comment Induction and Countable Set
@WhizKid Induction (in a just slightly different formulation than what you are accustomed to) works for all wellordered sets, for example for ordinal numbers, of which the set of natural numbers with standard order is just the smallest infinite example. In fact, these may even be uncountable!
Oct
11
answered Induction and Countable Set
Oct
11
revised Proof of index number in complex analysis
added 545 characters in body
Oct
11
answered Proof of index number in complex analysis
Oct
11
answered Mathematical Induction Can't get past base step… Please help
Oct
11
comment For a Gaussian Random walk where $x_n$ is the sum of $n$ normal random variables, what is $P(x_1 >0, x_2 >0)$?
Exactly. This geometric approach works because $e^{-x^2/2}\cdot e^{-y^2/2}$ is rotation symmetric.
Oct
11
awarded  Enlightened
Oct
11
awarded  Nice Answer
Oct
11
comment when $p \mid ab \Rightarrow p \mid a$ or $p \mid b$?
I'm no native speaker, but I assume separable should rather be called reducible.
Oct
11
answered What is the answer of this problem?
Oct
11
revised What is the answer of this problem?
added 1 characters in body
Oct
11
comment Prove that $\lim_{n \to\infty}{a_n}=L$, then $\{a_n\}$ is a Cauchy sequence
What you write starting from "First I suppose" looks rather like a proof attempt in the opposite direction: If $\{a_n\}$ is Cauchy, then it converges to some real number $L$.
Oct
11
answered Function of two integers that has not repeated values
Oct
11
comment How do Mathematicians send email?
I usually use (and I think it is not too uncommon) TeX-like syntax or in fact simplifications thereof working with spacing. E.g.: "For all x in R, we have sin x in [-1,1]."