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Sergey Dovgal
  • Member for 6 years, 1 month
  • Last seen more than a week ago
29 answers
251 votes
87k views
314 bookmarks
Mathematical games interesting to both you and a 5+-year-old child
65 answers
138 votes
32k views
152 bookmarks
Important formulas in combinatorics
1 answer
55 votes
5k views
42 bookmarks
IMO 2017/6 via arithmetic geometry
2 answers
45 votes
4k views
24 bookmarks
The two ways Feynman diagrams appear in mathematics
16 answers
43 votes
7k views
28 bookmarks
What does the generating function $x/(1 - e^{-x})$ count?
3 answers
18 votes
1k views
8 bookmarks
What is the probability that two random permutations have the same order?
1 answer
15 votes
980 views
2 bookmarks
Existence of double eigenvalue
1 answer
14 votes
643 views
6 bookmarks
For a stable matrix $B$ and anti-symmetric $T$, such that $B(I+T)$ is symmetric, show that $\mbox{tr}(TB)\leq0$
2 answers
12 votes
1k views
9 bookmarks
Eigenvalue perturbation theory via Feynman diagrams
2 answers
11 votes
1k views
4 bookmarks
Proofs of some combinatorial identities
1 answer
11 votes
483 views
2 bookmarks
Which of these sums appear most often?
1 answer
10 votes
608 views
4 bookmarks
$2 \times 2$ matrix question
2 answers
10 votes
774 views
5 bookmarks
Simple question about polynomials
2 answers
9 votes
730 views
4 bookmarks
Asymptotic difference between a function and its "binomial average"
3 answers
8 votes
1k views
3 bookmarks
Optimization problem with determinant as objective
0 answers
6 votes
98 views
4 bookmarks
A conjectured trace inequality for some products of powers of matrices II
1 answer
6 votes
261 views
3 bookmarks
Phase transition in matrix
0 answers
5 votes
186 views
2 bookmarks
a problem about possible generating series
0 answers
5 votes
176 views
2 bookmarks
How to count Isomorphism Types of arbitrary structures?
0 answers
4 votes
139 views
1 bookmarks
Using Mellin transform for a certain function
0 answers
3 votes
86 views
1 bookmarks
``de-polarizing" a univariate P-recurrence
1 answer
1 vote
233 views
2 bookmarks
Nonlinear low-rank approximation - corrected