New posts in extremal-combinatorics

Every $3\times 3$ square has even number of painted cells

combinatorics contest-math extremal-combinatorics

No sum of three numbers equals another number in set

combinatorics extremal-combinatorics

Minimum number of circles with 3 neighbors

geometry circles combinatorial-geometry extremal-combinatorics

More elegant proofs of $\binom a2+\binom b2\leq \binom{a+b-1}2$

combinatorics inequality binomial-coefficients combinatorial-proofs extremal-combinatorics

What is the best way to partition the $4$-subsets of $\{1,2,3,\dots,n\}$?

combinatorics coloring set-partition extremal-combinatorics

The drawn diagonals divide the $N\times N$ board into $K$ regions. For each $N$, determine the smallest and the largest possible values of $K$.

combinatorics graph-theory discrete-optimization planar-graphs extremal-combinatorics

Counting minimum elements needed such that their sum covers the whole finite space.

combinatorics finite-fields extremal-combinatorics

How many acute triangles can be formed by 100 points in a plane?

discrete-geometry extremal-combinatorics plane-geometry

Given $2^{n-1}$ subsets of a set with $n$ elements with the property that any three have nonempty intersection, prove that ....

linear-algebra combinatorics solution-verification contest-math extremal-combinatorics

Students who see ears of another student

combinatorics extremal-combinatorics

Partitions that separate all subsets

combinatorics extremal-combinatorics

N gunmen in a field

combinatorics geometry contest-math extremal-combinatorics

Which graphs can be drawn using straight lines with no disjoint edges?

discrete-mathematics graph-theory extremal-combinatorics planar-graphs

Searching radioactive balls

combinatorics optimization algorithms information-theory extremal-combinatorics

Split up $n \in \mathbb{N}$ into sum of naturals with maximum LCM

combinatorics sequences-and-series algorithms optimization extremal-combinatorics

Biggest Little Polyhedron

geometry polyhedra open-problem extremal-combinatorics combinatorial-geometry

Maximally dense Unit Distance Graphs

combinatorics graph-theory extremal-combinatorics tiling

Distinctness is maintained after adding some element to all sets

combinatorics extremal-combinatorics

Extremal combinatorics

combinatorics graph-theory extremal-combinatorics matching-theory extremal-graph-theory

Largest-area shape with diameter 1?

geometry optimization area extremal-combinatorics