Proof that the order of $D_n$ is $2n$
121880
How to show that $|D_{2n}| = 2n$ via the presentation?
1712
$ d_1,d_2\mid n\iff {\rm lcm}(d_1,d_2)\mid n\ $ [LCM Universal Property]
58863
Proof that $A_n$ the only subgroup of $ S_n$ index $2$.
52157
Prove that $d(n)\leq 2\sqrt{n}$
151553
Big-O proof showing that t(n) is O(1)
48393
Abelian groups of order n.
8742
Examples and further results about the order of the product of two elements in a group
144819
Proving $P(n) =n^{\phi(n)} \prod\limits_{d \mid n} \left(\frac{d!}{d^d} \right)^{\mu(n/d)}$
3703
Order of finite fields is $p^n$
79055
Orders of a symmetric group
62977
Show on $\mathbb{N}$ there are $2^{\aleph_0}$ nonisomorphic linear orders.
19599
$ d(x_n,y_n) \to d(x,y)$ if $x_n\to x$ and $y_n \to y$
129680
Prove that $n$ is even.
104549
When $d \mid n$, the number of elements of order $d$ in a cyclic subgroup of order $n$ is $\phi (d)$
48251
Prove that if $n \in \mathbb{N}$, then $\sum_{d|n}{(d(n))^3}=(\sum_{d|n}{d(n)})^2$ where $d(n)$ is the divisor function.
98514
Prove by induction that the number of derangements of length $n$ is $D_n = (n-1)(D_{n-1}+D_{n-2}), n>2$
79568
Cardinality of the set $D$