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New posts in combinatorics
Proof of a Combinatorial Abel Identity
sequences-and-series
combinatorics
discrete-mathematics
generating-functions
how many permutations of {1,2,...,9}
combinatorics
discrete-mathematics
permutations
What is known about the minimal number $f(n)$ of geometric progressions needed to cover $\{1,2,\ldots,n\}$, as a function of $n$?
sequences-and-series
combinatorics
elementary-number-theory
analytic-number-theory
geometric-progressions
Number of invertible matrices over finite rings
combinatorics
matrices
Permutations of a set that keep at least one integer fixed
combinatorics
permutations
Permutation with Duplicates
combinatorics
permutations
Combinatorial interpretation of Delannoy numbers formula
combinatorics
intuition
recurrence-relations
The number of permutations of $\{1,2,\ldots,n\}$ that have exactly one ascent (rise).
combinatorics
generating-functions
What is the expression for putting $n$ indistinguishable balls into $k$ indistinguishable cells?
combinatorics
discrete-mathematics
Positivity of the alternating sum associated to at most five subspaces
linear-algebra
combinatorics
vector-spaces
homological-algebra
combinatorial-geometry
de Bruijn sequence in which order of subsquences doesn't matter
sequences-and-series
combinatorics
Getting everyone to meet everyone else
combinatorics
discrete-mathematics
graph-theory
combinatorial-designs
Number of $n^2\times n^2$ permutation matrices with a 1 in each $n\times n$ subgrid
combinatorics
discrete-mathematics
Partition a set into g groups, k different ways, such that no pair of elements is ever in the same group together more than M times
combinatorics
reference-request
combinatorial-designs
Combinatorics proof (any set of 16 numbers from 1 to 100 contains repeated sums)
combinatorics
pigeonhole-principle
Formula for finite sum $\sum_{1\leq\alpha_{1}<\alpha_{2}<\ldots<\alpha_{k}\leq n}\frac{\alpha_{1}+\alpha_{2}+\ldots+\alpha_{k}}{k}$
combinatorics
summation
Isomorphism between $E_8$ lattice and lattice defined by Extended Hamming Code
linear-algebra
abstract-algebra
combinatorics
coding-theory
Stirling numbers combinatorial proof
combinatorics
discrete-mathematics
inclusion-exclusion
combinatorial-proofs
stirling-numbers
Find an infinite set of positive integers such that the sum of any two distinct elements has an even number of distinct prime factors
number-theory
combinatorics
graph-theory
Is there a closed form for the sum of the cubes of the binomial coefficients?
combinatorics
binomial-coefficients
closed-form
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