Number of permutations $\sigma\in S_n$ with $\sigma(k)\neq k$ for all $k=1,\ldots,n$
23701
I have a problem understanding the proof of Rencontres numbers (Derangements)
15396
Enumerating all subgroups of the symmetric group
115258
Find all positive integers $n$ such that $\phi(n)+\sigma(n)=2n$.
66842
Number of $n^2\times n^2$ permutation matrices with a 1 in each $n\times n$ subgrid
38809
In how many ways can the letters of word $PERMUTATIONS$ be arranged if there are always 4 letters between P and S?
46971
Number of surjections from $\{1,...,m\}$ to $\{1,...,n\}$
45939
For which $n≥2$ does there exist $\sigma\in A_n$ with $|\sigma| > n$
128834
Proving the number of even and odd permutations of a subgroup $H<S_{n}$ are equal, provided $H$ is not contained in $A_{n}$
21000
Calculating $\sum_{k=1}^nk(k!)$ combinatorially
24212
proving how many permutations exist.
73323
Permutations when some objects are alike
124224
How many groups of order $n$ with center {e} exist?
123567
Number of permutations which are products of exactly two disjoint cycles.
7938
Number of Homomorphisms from $\Bbb{Z}_m$ to $\Bbb{Z}_n$
142038
Finding the number of elements of order two in the symmetric group $S_4$
105911
The number of permutations of $\{1,2,\ldots,n\}$ that have exactly one ascent (rise).
148413
Proving $S_n$ is generated by the set $\{(1\text{ }2),(2\text{ }3),\cdots,(n-1\text{ }n)\}$ of $n-1$ transpositions.