User Stefan Kohl

119 votes

Examples of unexpected mathematical images

answered Aug 11, 2014 at 9:13

38 votes

Accepted

Does the equation $241+2^{2s+1}=m^2$ have a solution?

answered Sep 27, 2015 at 22:32

37 votes

PhD dissertations that solve an established open problem

answered May 20, 2018 at 18:59

33 votes

Accepted

Rational points on a sphere in $\mathbb{R}^d$

answered Mar 23, 2013 at 17:16

27 votes

Are there $n$ groups of order $n$ for some $n>1$?

answered Nov 28, 2015 at 13:41

22 votes

Small-index subgroups of SL(3,Z)

answered Feb 27, 2013 at 14:15

21 votes

When has the Borel-Cantelli heuristic been wrong?

answered Apr 16, 2015 at 22:32

18 votes

Why do sporadic simple groups have so few conjugacy classes?

answered Dec 15, 2014 at 19:01

17 votes

Is there an infinite group with exactly two conjugacy classes?

answered Nov 3, 2013 at 13:59

16 votes

The four-square theorem from the Gauss-Legendre three-square theorem

answered Mar 16, 2013 at 13:31

16 votes

Conjugacy classes of $\mathrm{SL}_2(\mathbb{Z})$

answered Apr 13, 2016 at 22:26

15 votes

Accepted

Lower density of {primes} times themselves

answered Jun 3, 2015 at 8:49

14 votes

How did Cole factor $2^{67}-1$ in 1903?

answered May 23, 2015 at 14:08

14 votes

Accepted

Lattice n-gons with ordered side lengths 1,2,3,...,n

answered Apr 30, 2016 at 13:53

14 votes

Accepted

Identify one group of linear transformations

answered May 1, 2017 at 9:41

14 votes

Is there an algorithm to solve quadratic Diophantine equations?

answered Sep 28, 2013 at 16:47

13 votes

Accepted

The set of orders of elements in a group

answered Jan 16, 2013 at 18:27

13 votes

Accepted

A question on Collatz's conjecture:proportion of "low flying" orbits

answered Feb 20, 2015 at 0:12

12 votes

Is there a way of canonically labelling permutation groups?

answered Apr 25, 2015 at 13:53

12 votes

About the proof of the proposition "there exists irrational numbers a, b such that a^b is rational"

answered Mar 24, 2015 at 9:48

12 votes

Accepted

Orders of Finite Simple Groups

answered Jul 4, 2014 at 17:45

12 votes

Ore's Conjecture for perfect groups

answered Sep 1, 2014 at 12:19

12 votes

Taking a theorem as a definition and proving the original definition as a theorem

answered Sep 27, 2021 at 12:45

12 votes

Perfect group of order 190080

answered Jan 5, 2016 at 17:19

11 votes

Is there a formula for the number of elements in $S_n$ having length $k$ with respect to the generators taken to be the transpositions?

answered Apr 16, 2016 at 16:01

11 votes

Accepted

Compute an arbitrary decimal place of $\pi$

answered Jul 25, 2014 at 21:30

11 votes

Accepted

Collatz stopping-time and Poisson distribution, and connection to other problems?

answered May 12, 2013 at 20:43

10 votes

Accepted

Finite groups for which the element orders form an arithmetic progression

answered Mar 3, 2014 at 10:11

10 votes

On Generalizations of Fermat's Conjecture

answered Oct 26, 2013 at 0:03

10 votes

Accepted

Can $b^4+1$ be a pseudoprime to base 2 (except for Fermat numbers)?

answered Mar 24, 2016 at 14:38

Stack Exchange Network

150 Answers

Examples of unexpected mathematical images

Does the equation $241+2^{2s+1}=m^2$ have a solution?

PhD dissertations that solve an established open problem

Rational points on a sphere in $\mathbb{R}^d$

Are there $n$ groups of order $n$ for some $n>1$?

Small-index subgroups of SL(3,Z)

When has the Borel-Cantelli heuristic been wrong?

Why do sporadic simple groups have so few conjugacy classes?

Is there an infinite group with exactly two conjugacy classes?

The four-square theorem from the Gauss-Legendre three-square theorem

Conjugacy classes of $\mathrm{SL}_2(\mathbb{Z})$

Lower density of {primes} times themselves

How did Cole factor $2^{67}-1$ in 1903?

Lattice n-gons with ordered side lengths 1,2,3,...,n

Identify one group of linear transformations

Is there an algorithm to solve quadratic Diophantine equations?

The set of orders of elements in a group

A question on Collatz's conjecture:proportion of "low flying" orbits

Is there a way of canonically labelling permutation groups?

About the proof of the proposition "there exists irrational numbers a, b such that a^b is rational"

Orders of Finite Simple Groups

Ore's Conjecture for perfect groups

Taking a theorem as a definition and proving the original definition as a theorem

Perfect group of order 190080

Is there a formula for the number of elements in $S_n$ having length $k$ with respect to the generators taken to be the transpositions?

Compute an arbitrary decimal place of $\pi$

Collatz stopping-time and Poisson distribution, and connection to other problems?

Finite groups for which the element orders form an arithmetic progression

On Generalizations of Fermat's Conjecture

Can $b^4+1$ be a pseudoprime to base 2 (except for Fermat numbers)?