Newbetuts

Can this enumeration problem be generalized? (counting $20$-subsets of $\{1,2,3,\dots 30\}$ with no three consecutive elements)

combinatorics contest-math

Number of permutations with restrictions

combinatorics discrete-mathematics permutations

Deleting rows and columns of a matrix probability

probability combinatorics

BMO2 2017 Question 4 - Bobby's Safe

combinatorics optimization contest-math combinatorial-game-theory

Combinatorics meaning of $L_m=\sum_{j=m}^{n}(-1)^{j-m}\binom{j-1}{m-1}S_j$

combinatorics inclusion-exclusion combinatorial-proofs

7 dancers on a circle

probability combinatorics

Relation between steps and turns in a simple symmetric random walk

probability combinatorics martingales expected-value random-walk

Combinatorial interpretation of the identity $(f \circ f \circ f)(x) = x$ where $f(x) = 1/(1-x)$ for $x\in(-1,1)$

combinatorics complex-analysis generating-functions mobius-transformation

Scores of black and white marks

combinatorics graph-theory

A Proof of Correctness of Durstenfeld's Random Permutation Algorithm

probability combinatorics permutations

Bijections from $A$ to $B$, where $A$ is the set of subsets of $[n]$ that have even size and $B$ is the set of subsets of $[n]$ that have odd size [duplicate]

combinatorics elementary-set-theory

How to prove $f(n)=\sum_{k=0}^n\binom{n+k}{k}\left(\frac{1}{2}\right)^k=2^n$ without using the induction method? [duplicate]

combinatorics algebra-precalculus

To find the total no. of six digit numbers that can be formed having property that every succeeding digit is greater than preceding digit. [closed]

combinatorics permutations

Description of flipping tableau for inversions in reduced decompositions of permutations

combinatorics group-theory coxeter-groups

New posts in combinatorics

Prove that all light bulbs can't light off

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

Help me to simplify $\sum\limits_{i=0}^{\lfloor\frac{r}{2}\rfloor}\binom{r}{i}\binom{r-i}{r-2i}$

Flip a coin 5 times. What is the probability that heads never occurs twice in a row?

A nice and hard colouring problem

On Covering $\{1,\cdots,n\}$ with Unions of Small Subsets

Can this enumeration problem be generalized? (counting $20$-subsets of $\{1,2,3,\dots 30\}$ with no three consecutive elements)

Number of permutations with restrictions

Deleting rows and columns of a matrix probability

BMO2 2017 Question 4 - Bobby's Safe

Combinatorics meaning of $L_m=\sum_{j=m}^{n}(-1)^{j-m}\binom{j-1}{m-1}S_j$

7 dancers on a circle

Relation between steps and turns in a simple symmetric random walk

Combinatorial interpretation of the identity $(f \circ f \circ f)(x) = x$ where $f(x) = 1/(1-x)$ for $x\in(-1,1)$

Scores of black and white marks

A Proof of Correctness of Durstenfeld's Random Permutation Algorithm

Bijections from $A$ to $B$, where $A$ is the set of subsets of $[n]$ that have even size and $B$ is the set of subsets of $[n]$ that have odd size [duplicate]

How to prove $f(n)=\sum_{k=0}^n\binom{n+k}{k}\left(\frac{1}{2}\right)^k=2^n$ without using the induction method? [duplicate]

To find the total no. of six digit numbers that can be formed having property that every succeeding digit is greater than preceding digit. [closed]

Description of flipping tableau for inversions in reduced decompositions of permutations