Number Theory Example of a UFD that is not a PID
129305
Is any UFD also a PID?
79417
A "non-trivial" example of a Cauchy sequence that does not converge?
73702
What are examples of irreducible but not prime elements?
135610
How to give an example of a $f$ differentiable in a deleted neighborhood of $x_0$ such that $\lim_{x\to x_0}f^\prime(x)$ doesn't exist?
111679
Example of a ring without unity that has a subring with unity?
150605
Existence of a regular uncountable $\aleph_{\alpha}$ without $\mathsf{AC}$
34798
Example of element of double dual that is not an evaluation map
59279
Example of function that is differentiable, but the second derivative is not defined
24988
Prove there exists $m > 2010$ such that $f(m)$ is not prime
4946
Non-existence of irrational numbers?
13961
An example of a lattice that's not totally ordered
143343
The series of reciprocals of the integers that do not contain 9 in their decimal representation
147366
What are a few examples of noncyclic finite groups?
57138
Localization of a UFD that is a PID
126199
Proof of $\pi$ not being a quadratic irrational number.
133495
Example of a ring without Invariant Basis Property
100436
Examples of nowhere continuous functions