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Questions designed to generate a "big list" of certain results, examples, conjectures, etc. via many individual answers, each contributing one or a few instances. Such a question should typically be in Community Wiki mode (CW); after asking, please, flag for moderators attention requesting the question to be made CW.

2 votes

Tweetable Mathematics

Sz(q) has two orbits more than PSL(2,q) under the action of its automorphism group - see https://doi.org/10.1081/AGB-120004501, Thm. 3.4.
3 votes

The half-life of a theorem, or Arnold's principle at work

An example which shows that even MathOverflow does not always prevent a theorem from being forgotten and rediscovered later is the following assertion which has been proved by G. A. Miller [1] in 1900 …
1 vote

Breakthroughs in mathematics in 2021

The negative answer by counterexample to the Modular Isomorphism Problem for group rings (that is, the question whether for $p$-groups $G$ and $H$, the group rings ${\mathbb F}_p G$ and ${\mathbb F}_p …
10 votes

When is 2 qualitatively different from 3?

Let $G$ be a finite group. If the order of $G$ is not divisible by 2, then $G$ is solvable; if it is not divisible by 3, then no such conclusion can be drawn.
3 votes

Examples of eventual counterexamples

$1223$ is the smallest odd prime which does not divide any Carmichael number with $3$ prime factors -- cf. e.g. here.
3 votes

Examples of eventual counterexamples

While there is no known counterexample to the assumption that the probabilistic Baillie–PSW primality test is actually a proper primality test, there is strong evidence that there exist such counterex …
7 votes

Examples of eventual counterexamples

Let $Q(n), n \in \mathbb{N}$ denote Hofstadter's Q sequence -- i.e. $Q(1) = Q(2) = 1$, and $Q(n) = Q(n-Q(n-1)) + Q(n-Q(n-2))$ for $n > 2$. Then we have: $Q(3 \cdot 2^0) = 2$, $Q(3 \cdot 2^1) = 4$, $Q …
0 votes

Modern results that are widely known, yet which at the time were ignored, not accepted or cr...

Although strictly meanwhile more than 99 years old, a well-known example here are the Julia- and Fatou sets. -- These sets were first investigated by Gaston Julia and Pierre Fatou in 1917/18, but this …
5 votes
1 answer
493 views

Nice diophantine equations with large smallest solutions

Given a polynomial $P$ with integer coefficients in finitely many variables, we denote by $v(P)$ the product of the absolute values of the non-zero coefficients and the non-zero total degrees of the m …
7 votes

Examples of eventual counterexamples

Assertion: Every integer greater than 1 can be written as the sum of a prime number and a perfect power of a nonnegative integer. The smallest (and maybe only?) counterexample to this assertion is $11 …
1 vote

Examples of eventual counterexamples

Numerically, one finds that the function $$ f(n) \ := \ \sum_{p \leq n, \\ p \ \text{prime}} \frac{1}{p} \left(1 - \frac{1}{\ln(\ln(p))}\right) $$ appears to take its maximum at $n = 2$. While alr …
37 votes

PhD dissertations that solve an established open problem

The thesis of Martin Hertweck answered the at that time 60-years-old isomorphism problem for integral group rings in the negative, by constructing a counterexample. That is, a pair of non-isomorphic f …
4 votes

Examples of unexpected mathematical images

Explanation: Let $r(m)$ denote the residue class $r+m\mathbb{Z}$, where $0 \leq r < m$. Given disjoint residue classes $r_1(m_1)$ and $r_2(m_2)$, let the class transposition $\tau_{r_1(m_1),r_2(m_2 …
73 votes
17 answers
9k views

Mathematical research published in the form of poems

The article Friedrich Wille: Galerkins Lösungsnäherungen bei monotonen Abbildungen, Math. Z. 127 (1972), no. 1, 10-16 is written in the form of a lengthy poem, in a style similar to that of the work …
119 votes

Examples of unexpected mathematical images

One can obtain a nice picture showing somewhat unexpected patterns by marking all rational points on the unit sphere whose coordinates have denominator less than some upper bound, and projecting this …

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