New posts in combinatorics

Choosing 5 elements from a set of 13

How many ordered quadruples of positive integers $\{a,b,c,d\}$ are there such that $a\leq b\leq c\leq d\leq 50$ and $a+b+c+d=100$?

Counting minimum elements needed such that their sum covers the whole finite space.

combinatorics finite-fields extremal-combinatorics

"Ballot numbers" sum up to Catalan numbers

combinatorics trees catalan-numbers

Ratio of $2$-norm to infinity norm of coefficients in the expansion of $(1+𝑥+𝑥^2+\ldots+x^m)^n$?

combinatorics polynomials asymptotics multinomial-coefficients

Does this double series converge?

real-analysis combinatorics sequences-and-series summation

Prove there are at least $2$ lines with the property that each of them divides the plane into $2$ regions with the same number of red and blue points. [duplicate]

combinatorics geometry puzzle

Prove $30|(a^3b-ab^3) $

Prove that $\sum_{n=0}^N\binom{2N-n}N2^n(n+1)=(1+2N)\binom{2N}N$

combinatorics summation

Does $K_{12,12}$ decompose into $K_{4,4}-I$ subgraphs?

combinatorics discrete-mathematics graph-theory

Combinatorial interpretation of Euclid's form for even perfect numbers

combinatorics number-theory perfect-numbers

Permutation - how to order 6 elements out of 13 with 3 conditions

combinatorics permutations combinations

How many matrices in $M_n(\mathbb{F}_q)$ are nilpotent?

combinatorics matrices

Kings on a chessboard

combinatorics puzzle

$32$ Goldbach Variations - Papers presenting a single gem in number theory or combinatorics from different point of view

combinatorics number-theory reference-request big-list

How long does a sequence need to be to be guaranteed to have a monotonic subsequence length k?

sequences-and-series combinatorics order-theory ramsey-theory

Matching Hats AND Coats Problem

probability combinatorics

What does this list permutations implementation in Haskell exactly do?

list haskell permutation combinatorics

Proof of the duality of the dominance order on partitions

combinatorics integer-partitions alternative-proof

How do I prove that $2^n=O(n!)$?

combinatorics asymptotics