New posts in combinatorics

Number of triangles formed by $m$ lines

combinatorics geometry

Placing $9$ black and $9$ white rooks on $ 6\times6$ board without any attacks between different colours

combinatorics contest-math

Any $B \subset \{10,11,...,99\}$, with $|B| =10$ has two subsets such that $\sum_{a \in B_1} a = \sum_{b \in B_2} b$

combinatorics discrete-mathematics pigeonhole-principle

Generating function for gamma function (or factorial)

combinatorics generating-functions factorial gamma-function

Which concept is more general, Cartesian Product or Rule of Product or Direct Product?

combinatorics elementary-set-theory

Fibonacci numbers divisible by $9$

combinatorics elementary-number-theory discrete-mathematics fibonacci-numbers

1965 Putnam, B2

combinatorics contest-math

Prove that the intersection of all the sets is nonempty.

Graph with even vertices and ${n-1}\choose 2$ $+ 1$ edges has a perfect matching

combinatorics discrete-mathematics graph-theory hamiltonian-path matching-theory

Properties of sequence

sequences-and-series combinatorics proof-writing

How to prove Euler's pentagonal theorem? Some hints will help

number-theory combinatorics complex-analysis

How to simplify complicated Recursion.

Scheduling a team based activity with 10 different teams and X different games. Every team must meet each other ONCE but never twice,

number of binary solutions under linear restrictions

combinatorics reference-request binary-programming

How to solve second degree recurrence relation?

combinatorics recurrence-relations generating-functions summation

Number of divisors of the form $(4n+1)$

combinatorics algebra-precalculus elementary-number-theory

How many bit strings of length 8 start with "1" or end with "01"?

combinatorics discrete-mathematics computer-science inclusion-exclusion bit-strings

Calculating the probability of combinations with unequal probabilities for each element

probability combinatorics

How many group combinations of 3 can I make of 6 people?

Are the error terms of the partial sums of inclusion-exclusion unimodal?

combinatorics elementary-set-theory inclusion-exclusion