New posts in combinatorics

Proving that $\sum_{a=1}^{b} \frac{a \cdot a! \cdot \binom{b}{a}}{b^a} = b$

combinatorics summation induction binomial-coefficients

How to distinguish between combination and permutation questions?

combinatorics discrete-mathematics permutations combinations

Equations with factorials

combinatorics

Books for maths olympiad

combinatorics geometry number-theory contest-math book-recommendation

How many 0's are in the end of this expansion?

combinatorics elementary-number-theory divisibility contest-math number-systems

40 Vertices And A Connected Graph, Minimum Number Of Edges?

combinatorics graph-theory connectedness

Toward Explicit Formula from Recursion : Is Generating function "the only" answer?

combinatorics recurrence-relations generating-functions recursion

Paths in a square grid with diagonal moves allowed

combinatorics

Given a list of n integers, find the minimum cardinality subset with sum greater than or equal to x

algorithm optimization dynamic-programming combinatorics subset-sum

Choosing at least 2 women from 7 men and 4 women

combinatorics

Looking for different proofs of "Discrete Liouville's Theorem".

combinatorics complex-analysis functional-analysis probability-theory functions

Probability that sheepdog performs at least one task successfuly - Am I doing this problem right?

probability combinatorics

On the problem $1$ of Putnam $2009$

contest-math combinatorics geometry

Number of subsets when each pair of distinct elements is contained in exactly one subset

linear-algebra combinatorics

Sparse Ruler Conjecture

combinatorics number-theory graph-theory

The number of ways to order 26 alphabet letters, no two vowels occurring consecutively

combinatorics discrete-mathematics permutations

Picking Multiples of 4

probability combinatorics

Ms Black, Ms Blue and Ms Green - Is there really a unique answer?

combinatorics

What is the coefficient of the $x^3$ term in the expansion of $(x^2+x-5)^7$ (See details)?

combinatorics algebra-precalculus multinomial-coefficients

Why is this weighted sum of binomials with alternating signs simplifies?

combinatorics summation binomial-coefficients