$1989$ Russian Mathematical Olympiad
49509
A number $n$ has $12$ divisors and $d_{d_4-1} = (d_1+d_2+d_4)d_8$.
33737
Does $1.0000000000\cdots 1$ with an infinite number of $0$ in it exist?
130610
Book recommendation : Olympiad Combinatorics book
47079
A Russian girl is asking for 500 euros to get a passport in Russia. Is this a realistic amount of money for a passport fee?
38254
Trigonometry Olympiad problem: Evaluate $1\sin 2^{\circ} +2\sin 4^{\circ} + 3\sin 6^{\circ}+\cdots+ 90\sin180^{\circ}$
146534
Find out trace of a given matrix $A$ with entries from $\mathbb{Z}_{227}$
140364
Covering ten dots on a table with ten equal-sized coins: explanation of proof
54871
Sum of numbers on chessboard.
104982
Determine $\phi(2^{399}+1)$
8476
Proof of the Hockey-Stick Identity: $\sum\limits_{t=0}^n \binom tk = \binom{n+1}{k+1}$
107319
$F=ma$ contest problem on angular momentum
59675
A inequality proposed at Zhautykov Olympiad 2008
136652
Closed form expression for the product $\prod\limits_{k=1}^{n}\left(1 - \frac{1}{ak}\right)$
44715
Exact value for $\cos 36°$
68080
Evaluation of $\sum_{k=0}^n{n\choose k}^2u^k$
118130
Mathematical notation around the world
116379
What are the last two digits of $2017^{2017}$?