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23
Which person is telling the truth?
puzzling.stackexchange.com

23
A finite alternating sum
mathoverflow.net

21
The $2\pi$ in the definition of the Fourier transform
mathoverflow.net

20
Prime tree game
puzzling.stackexchange.com

19
Inverse of special upper triangular matrix
mathoverflow.net

18
Harmonic sums and elementary number theory
mathoverflow.net

16
Board with all 2020s
puzzling.stackexchange.com

15
The Blank Sudoku
puzzling.stackexchange.com

15
Prove that $x$ is an integer if $x^4-x$ and $x^3-x$ are integers.
math.stackexchange.com

13
Evaluate $\lim\limits_{n \to \infty}\frac{(-1)^n}{n!}\int_0^n (x-1)(x-2)\cdots(x-n){\rm d}x$
math.stackexchange.com

13
Happy $\pi$-day! Is it true that $\sum_{p \;\text{prime} } \frac{1}{{\pi}^p} < \pi -\lfloor \pi \rfloor$?
math.stackexchange.com

13
Is it true that $\sum_{k=m}^n\frac{\sigma(k)}k\not\in\mathbb Z$ for all derangements $\sigma\in S_n$ and $1\le m\le n$?
mathoverflow.net

13
Sudokus everywhere!
puzzling.stackexchange.com

12
Number of paths on $\mathbb Z^d$
math.stackexchange.com

11
Is it possible to split the natural numbers into a finite number of sets so that no pair of numbers within a set adds up to a square?
math.stackexchange.com

10
Evaluate the following integral $ \int_1^{\infty} \frac{\lbrace x\rbrace-\frac{1}2}{x} dx$
math.stackexchange.com

10
End(M) for cyclic R-module M is a commutative ring where R is a PID.
math.stackexchange.com

10
Colombian Sudoku
puzzling.stackexchange.com

10
A rectangle, a circle, and a triangle are drawn on a plane
puzzling.stackexchange.com

10
Connect Wall: “Who's that Pokémon?”
puzzling.stackexchange.com

10
To equip hand sanitizers
puzzling.stackexchange.com

9
The beginning of a factorial
puzzling.stackexchange.com

9
If $x_{n+1}= \frac{nx_{n}^2+1}{n+1}$ then $x_{n}=1$
mathoverflow.net

9
Partition of [3n] into summoids
mathoverflow.net

9
There at least 4 divisors of $n-1$ which do not divide $\phi(n)$ if $n$ is a composite of the form $6k+1$
mathoverflow.net

8
Prove that $x^3+2y^3+4z^3\equiv6xyz \pmod{7} \Rightarrow x\equiv y\equiv z\equiv 0 \pmod{7}$
math.stackexchange.com

8
Two button calculator part 2
puzzling.stackexchange.com

8
A bound of the harmonic series of squares.
math.stackexchange.com

8
Paying bills in Alphagonia
puzzling.stackexchange.com

8
Find the limit $\lim\limits_{n \to \infty} \frac {n!} {1 \cdot 3 \cdot 5 \cdots (2n-1)}.$
math.stackexchange.com

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