Why is $|\mathbb N | = |\mathbb Z|$?
141073
Are there fewer positive integers than all integers?
132470
Does $\mathbb R^2$ contain more numbers than $\mathbb R^1$?
63183
Suppose $a,b,m,n$ are natural numbers, prove that if $a({m \over n})=b$ and $(a,n)=1$, then ${m \over n} \in \mathbb{N}$
83116
Uncountability of basis of $\mathbb R^{\mathbb N}$
66020
What is $\mathbb Z[[t]]$? What are the double brackets?
86015
$\mathbb Q[x]/(x^2+1)$ is not isomorphic to $\mathbb Q[x]/(x^2+2)$
144105
Ring homomorphism from $\mathbb Z$ to $\mathbb Z$ is always identity or $0$
35691
$\mathbb Z[\sqrt 3]$ contains infinitely many units
65391
Prove by induction. $n \in \mathbb N$.
133636
Is $\mathbb Z[X]/(X^2-1)$ a domain?
59459
Binary sequences and ${2}^{\mathbb{N}}$ have the same cardinality
32108
$ a\in \Bbb Z_n$ is invertible $\,\Rightarrow\gcd (a,n) =1$
118073
Is the ring $m\mathbb{Z}$ isomorphic to the ring $n\mathbb{Z}$?
117688
Prove that $\def\Aut{\operatorname{Aut}}\Aut(\mathbf{Z_{n}})\simeq \mathbf{Z_{n}^{*}}$
154305
Let $\pi$ denote a prime element in $\mathbb Z[i], \pi \notin \mathbb Z, i \mathbb Z$. Prove that $N(\pi)=2$ or $N(\pi)=p$, $p \equiv 1 \pmod 4$
5223
$\mathbb{Z}_m \times \mathbb Z_n$ is cyclic if and only if $\gcd(m,n)=1$
16507
Is $\mathbb{Z}= \{\dots -3, -2, -1, 0 ,1 ,2 , 3, \dots \}$ countable?