New posts in combinatorics

Probability of landing on the nth stair.

probability combinatorics random-walk

What are the number of ways of seating $n$ people around a circular table labelled from $1$ to n such that $3$ of them must be seated together?

combinatorics permutations

Generating ordered combination of numbers [closed]

sequences-and-series combinatorics

What is the probability that $m$ is the largest number drawn?

probability combinatorics

Probability that $2^a+3^b+5^c$ is divisible by 4

probability combinatorics divisibility

Concatenate values of n arrays in php

php arrays concatenation combinatorics

In how many ways are we able to arrange $k$ identical non-overlapping dominoes on a circle of $2n$ labelled vertices?

Solving a recurrence relation with the characteristic polynomial

combinatorics sequences-and-series characteristic-functions

Applying Burnside's Lemma to a Permutational Problem.

combinatorics group-theory permutations finite-groups group-actions

Sum numbers game with numbers $n,n-1,n-2,\ldots,3,2,1,2,3,\ldots,n-2,n-1,n$

combinatorics recreational-mathematics puzzle combinatorial-game-theory

How many positive integers less than 1,000,000 have the sum of their digits equal to 19?

combinatorics permutations combinations

How many entries in $3\times 3$ matrix with integer entries and determinant equal to $1$ can be even? [duplicate]

combinatorics matrices determinant

501 distinct coprime integers between 1 and 1000?

combinatorics pigeonhole-principle

To prove: $n!=\sum\limits_{r=0}^n (-1)^r \binom{n}{r} (n-r)^n$ [duplicate]

linear-algebra abstract-algebra combinatorics permutations

How do I prove the negative binomial identity?

combinatorics binomial-coefficients

How many three digit numbers with increasing digits can be formed from the set $\{1, 2, 3, 4, 5, 6, 7, 8\}$?

Stirling number of the first kind: Proof of Recursion formula

combinatorics stirling-numbers recurrence-relations

Why, when generating $N$ random numbers between $0$ and $N-1$, the number of unique numbers is always around $0.63N$?

How many unique combinations can I make with 18 elements (2a, 2b, 2c, 3d, 4e, 5f) that I distribute into 6 groups of 3?

How many ordered pairs $(A,B)$ they are if $A$ and $B$ are subsets of $\{ 1,2,3,4,5 \}$ such that $A \cap B = \{1\}$?