New posts in combinatorics

proof that $1 = \sum\limits_{k=0}^n (-1)^k { 2n \choose n,k,n-k } \frac{n}{n+k}$

combinatorics binomial-coefficients

4 by 4 Matrix Puzzle

combinatorics matrices puzzle

2D Rubik's cube?

abstract-algebra combinatorics group-theory

How many inequivalent ways to paint $n$ equally spaced points on a circle with $m$ colors? [duplicate]

combinatorics group-theory

Prove $\binom{3n}{n,n,n}=\frac{(3n)!}{n!n!n!}$ is always divisible by $6$ when $n$ is an integer.

combinatorics multinomial-coefficients

$4$ letter words taken from the letters of CONCENTRATIONS

combinatorics permutations combinations

Expected length of the largest repeating substring given a distinct digit/character [duplicate]

probability combinatorics

Colored Blocks Factorial

combinatorics factorial

Constructing numbers from basic arithmetic on digits

combinatorics number-theory elementary-number-theory

combinatorial proof of summation

combinatorics discrete-mathematics summation combinatorial-proofs

How many legal states of chess exists?

combinatorics game-theory

Probability of 2 or more students from a group of 5 being on the same team of 6 in a class of 36

How to explain the division rule in counting problem in a easy way?

Build Tree by Prüfer Code $(6,2,2,6,2,5,10,9,9)$

combinatorics graph-theory trees

How many ways can $5$ rings be placed on $4$ fingers?

Combinations of colored balls.

combinatorics combinations

In how many ways you can sit $n$ men and $n$ women so that :

combinatorics discrete-mathematics

Combinatorial proof of $\sum_{k=1}^n k^2 =\binom{n+1}{3} + \binom{n+2}{3}$

combinatorics discrete-mathematics

Distinct matrices of size $n\times n$ such that every row and column contains at least one $'a'$

combinatorics matrices

Combination problem [closed]