New posts in combinatorics

probability that no two spiders end up at the same vertex?

probability combinatorics

How many rectangles or triangles.

combinatorics discrete-mathematics recreational-mathematics

How many solutions does the equation $\sum_{i=1}^{k}{x_i}=c$ have, given that the $x_i\in\mathbb{Z}$ and $0\leq x_i\leq d$?

combinatorics discrete-mathematics permutations combinations inclusion-exclusion

The number of families of subsets of $\{1,2,...,n\}$ whose union is not the whole set.

general-topology combinatorics elementary-set-theory

Does in plane exist $22$ points and $22$ such circles that each circle contains at least $7$ points and each point is on at least $7$ circles.

linear-algebra combinatorics matrices contest-math algebraic-combinatorics

Make all cells of the square be the same color

combinatorics

How do I calculate how many ways 14 non-attacking bishops can be placed on a chessboard?

combinatorics recreational-mathematics

Combinatorial proof of $\binom{nk}{2}=k\binom{n}{2}+n^2\binom{k}{2}$

combinatorics discrete-mathematics binomial-coefficients combinatorial-proofs

Combinatorics problems that can be solved via infinite descent

combinatorics number-theory big-list infinite-descent

Combinatoric formula summing one

probability combinatorics summation binomial-coefficients game-theory

Proof of Dobinski's formula for Bell numbers

combinatorics stirling-numbers

Last coupon collected in the coupon collectors problem

probability combinatorics

Choosing a linear map $(\mathbb{Z}/2\mathbb{Z})^n \rightarrow \mathbb{Z}/2\mathbb{Z}$ which is nonzero on half of a sequence of vectors

linear-algebra combinatorics

Proving that $\sum_{k=0}^n\frac{1}{n\choose k}=\frac{n+1}{2^{n+1}}\sum_{k=1}^{n+1}\frac{2^k}{k}$

combinatorics summation binomial-coefficients fractions

Graph partition that span a third of edges

combinatorics graph-theory bipartite-graphs

Edgematching tiles

combinatorics recreational-mathematics puzzle tiling

How many ways are there to fill up a $2n \times 2n$ matrix with $1, -1$?

combinatorics permutations combinations

How many such ways to group 2n students?

combinatorics

Intuitive/Visual proof that $(1+2+\cdots+n)^2=1^3+2^3+\cdots+n^3$ [duplicate]

combinatorics proof-without-words

What is the probability of finding a sorted sequence of length $L$ in an array of $N$ randomly generated numbers?

probability combinatorics probability-theory