Paradox with squares and Pythagoras
2786
The staircase paradox, or why $\pi\ne4$
106716
The sum of square roots of non-perfect squares is never integer
19976
Riddle (simple arithmetic problem/illusion)
47697
Russell's paradox: a set cannot contain its own powerset
151326
Concurrency of the heights of a tetrahedron with opposite edges perpendicular.
125702
There is a square $Q$ consisting of $(0,0), (2,0), (0,2), (2,2)$
129693
An interesting problem with "decomposing" natural numbers.
18932
Squares in arithmetic progression
115391
A paradox of length contraction
116283
How to properly interpret a seemingly contradictory result in Mathematica?
22973
Show that an integer of the form $8k + 7$ cannot be written as the sum of three squares.
119304
Latin Square and Graph Theory
141101
Russia (2000) contest:Prove the existence of a pair of rows and columns with intersections differently coloured
84220
Questions on perfect squares
38167
What do I do when two squares are equally valid?
121063
Mathematics of Tetris 2.0
7919
The pigeonhole principle - how to solve questions like that?