A not free $\mathbb{Z}$-module
2719
Why isn't an infinite direct product of copies of $\Bbb Z$ a free module?
73825
Every $R$-module is a quotient of a free module
40996
Proving that free modules are flat (without appealing projective modules)
104486
Ideal in $\mathbb Z[x]$ which is not two-generated
137285
Prove $\mathbb{Z}_2 \times \mathbb{Z}_2$ is not isomorphic to $\mathbb{Z}_4$
80211
Annihilator of quotient module M/IM
137029
Prove that $\operatorname{Hom}_{\Bbb{Z}}(\Bbb{Q},\Bbb{Z}) = 0$ and show that $\Bbb{Q}$ is not a projective $\Bbb{Z}$-module.
17978
Isomorphism classes of $\mathbb{Z}[i]$ modules.
26368
Finitely generated graded modules over $K[x]$
92703
Proving that $\mathbb{Z}[x]$ and $\mathbb{Q}[x]$ are not isomorphic.
116943
Proof for maximal ideals in $\mathbb{Z}[x]$
85032
$Q(\mathbb{Z}[t]) / \mathbb{Z}[t]$ is not injective
9794
Quotient ring of Gaussian integers $\mathbb{Z}[i]/(a+bi)$ when $a$ and $b$ are NOT coprime
64130
Prove that $\mathbb{Q}^{\times}$ not isomorphic to $\mathbb{Z}^{n}$
85586
Proving $\mathbb{Q}$ isn't homeomorphic to $\mathbb{Z}$
6646
A (non-artificial) example of a ring without maximal ideals
120594
$\mathbb Z[i]/ \langle 1+2i \rangle \cong \mathbb Z_5$