Surjective map from $\mathbb{Z}^+$ to $\mathbb{Z}$.
119549
Prove the even integers are countable (by explicitly giving a bijection $\mathbb{N} \to E$)
93031
How to show that $\mathbb{Z}$ with the operation $m*n=m+(-1)^m n$ is associative?
113109
Showing that a map is bijective and finding its inverse
5906
All group homomorphism from $ \mathbb{Z} _m $ to $\mathbb{Z}_n $
5699
The number of ring homomorphisms from $\mathbb{Z}_m$ to $\mathbb{Z}_n$
123467
Prove that $f(z) = e^z$ maps $\mathbb{C} \setminus B $ onto $\mathbb{C} \setminus \{0\}$.
138275
Show $100+t$ is reducible in $\mathbb{Z}[[t]]$
20199
Find a surjective function $f:\mathbb{N}\to \mathbb{Q}$
16610
Surjectivity of a map from a space to itself
44670
Find all functions $f: \mathbb Z \to \mathbb Z$ such that $f(x+y)=f(x)+f(y)$
118299
Show that $(\mathbb{Z}[x]/(x^{n+1}))^{\times}\cong \mathbb{Z}/2\mathbb{Z}\times\Pi_{i=1}^n\mathbb{Z}$
89415
Number of homomorphisms from $(\mathbb Q^+ , \,\cdot\,)$ to $(\mathbb Z_n , +)$
51695
Finding all homomorphisms between $\mathbb{Z}/m\mathbb{Z}$ and $\mathbb{Z}/n\mathbb{Z}$
155745
Ideals of $\mathbb{Z}[X]$
73047
Proving surjectivity of $\cos(z)$ and $\sin(z)$ and find all $z : \cos(z) \in \mathbb R$ and all $z: \sin(z) \in \mathbb R$
83001
Easier way to show $(\mathbb{Z}/(n))[x]$ and $\mathbb{Z}[x] / (n)$ are isomorphic
104562
Prove that $\mathbb{Z}$ is not isomorphic to additive group of any vector space over any field.