Are there any integers $n$ such that $\sigma_0(n) = n$?
122961
Upper limit for the Divisor function
150677
What are the integers $n$ such that $\mathbb{Z}[\sqrt{n}]$ is integrally closed?
117862
Number of partitions of an $n$-element set into $k$ classes
108691
Characterize the natural numbers $n$ such that there is a surjective group homomorphism from $S_n$ to $S_{n-1}$.
35140
Existence of minimal $\sigma$-algebra and transfinite induction
67208
Can we say that there exist an integer $n$ such $A+nB$ invertible?
38946
Show that $\{\cup_{n\in K} (n, n+1]: K \subset \mathbb{Z}\}$ is a $\sigma$-algebra on $\mathbb{R}$
115860
Is a measure for a sigma algebra determined by its values for a generator of the sigma algebra?
26233
$[K(\zeta_n):K]=\phi(n)$?
4512
Is there a direct, elementary proof of $n = \sum_{k|n} \phi(k)$?
65098
Number of $\sigma$  -Algebra on the finite set
39409
$X_1,...,X_n$ be independent RVs and $X_i \perp \mathcal F $ for $1\ \leq \forall i \leq n$. Show that $\sigma (X_1,...,X_n) \perp \mathcal F$
73869
$\mathcal{C}_1 \subseteq \mathcal{C}_2 \implies \sigma( \mathcal{C}_1) \subseteq \sigma( \mathcal{C}_2) $
117133
Is there an infinite countable $\sigma$-algebra on an uncountable set
112182
Sequence of positive integers such that their reciprocals are in arithmetic progression
139622
Generator of rational functions unchanged under $\sigma(X) = X + 1$
28468
Haar measure on $SO(n)$