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Berci's user avatar
Berci's user avatar
Berci
  • Member for 11 years, 8 months
  • Last seen more than a week ago
68 votes
Accepted

Factorial, but with addition

53 votes

Is $2^{218!} +1$ prime?

31 votes
Accepted

Is $x^4+4$ an irreducible polynomial?

31 votes
Accepted

Joke explanation: "a comathematician is a device for turning cotheorems into ffee"

27 votes

Formal proof for $(-1) \times (-1) = 1$

22 votes

What is the correct spelling of Paul Erdős's name?

20 votes
Accepted

Pullback in $\mathrm{TOP}$

20 votes
Accepted

What is the opposite category of $Set$?

20 votes
Accepted

Can the map sending a presentation to its group be considered as a functor?

18 votes
Accepted

Understanding the ideal generated by a polynomial

17 votes
Accepted

There exists only two groups of order $p^2$ up to isomorphism.

17 votes

$\mathbb{C}\mathbb{P}^1$ is homeomorphic to $S^2$

16 votes
Accepted

Writing $28913000$ as the sum of two squares

15 votes

Variation of Pythagorean triplets: $x^2+y^2 = z^3$

14 votes
Accepted

The real projective space $\mathbb{R}P^{n}$ is second countable.

14 votes
Accepted

How to show that Hausdorff distance is a metric on the set of all compact non-empty subsets of a Polish space?

14 votes
Accepted

Prove that $\operatorname{rank}(A) + \operatorname{rank}(B) \ge \operatorname{rank}(A + B)$

14 votes
Accepted

Prove that the centralizer is a normal subgroup.

14 votes

To prove a sequence is Cauchy

14 votes
Accepted

Order of an element in a finite Group

13 votes
Accepted

If $f^2=f$, then $f$ is of constant rank.

13 votes
Accepted

How to prove Poisson Distribution is the approximation of Binomial Distribution?

13 votes
Accepted

Why can't $\sqrt{2}^{\sqrt{2}{^\sqrt{2}{^\cdots}}}>2$?

13 votes
Accepted

Sequence of continuous functions converges uniformly. Does it imply the limit function is continuous?

13 votes
Accepted

If $a+b=x$ and $ab=y$, what is the quickest way to solve for $a$ and $b$?

13 votes

Why is an empty set not a terminal object in categories $\mathsf{Top}$ and $\mathsf{Sets}$?

12 votes

Proof: How to prove $n$ is odd if $n^2 + 3$ is even

12 votes

a problem on a special root of $x^{11}-1=0$

12 votes
Accepted

A strictly positive operator is invertible

12 votes

How to prove that homomorphism from field to ring is injective or zero?

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