List questions from combinatorial-proofs

Published on 23 Mar 2026 - 12:05

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The VC dimension of convex d-gons

Published on 25 Mar 2026 - 7:48

90

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Number of distinct strings 'covering' all strings of same length, with restricted index selection.

Published on 28 Jun 2018 - 16:26

727

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All distinct k-permutations of length n, with repetitions

Published on 01 Jul 2018 - 23:55

129

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Counting binary sequences satisfying a certain condition

Published on 04 Jul 2018 - 0:39

85

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How can I deduce (3.6) from (3.5)?

Published on 25 Mar 2026 - 3:19

55

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$k$-out-of-$n$ combinations, arranged as matrices, satisfying certain conditions

Published on 07 Jul 2018 - 17:34

108

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Combinatorial proof of $ \sum_{k=0}^{n}\frac{1}{\binom{n}{k}} = \frac{n+1}{2^{n+1}}\sum_{k=0}^{n}\frac{2^{k+1}}{k+1}$

Published on 11 Aug 2018 - 13:40

200

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Proving that $\sum_{n=0}^r (-1)^n \binom{r}{n} (s+r-n-1)!/(s-n)! = 0$ without Taylor expansion

Published on 26 Aug 2018 - 18:23

83

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What is the maximal value that we can have after 99 operations?

Published on 25 Mar 2026 - 9:27

104

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How can I represent following series as a formula?

Published on 11 Sep 2018 - 23:22

182

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Proof of a combination identity: $\sum\limits_{i=0}^m\sum\limits_{j=0}^m\binom{i+j}{i}\binom{2m-i-j}{m-i}=\frac {m+1}2\binom{2m+2}{m+1}$

Published on 12 Sep 2018 - 12:49

215

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Combinatorics contest math question

Published on 13 Sep 2018 - 5:59

164

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Derangement with constraints

Published on 25 Sep 2018 - 17:40

578

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Proving formula sum of product of binomial coefficients

Published on 27 Sep 2018 - 9:10

List Question

Choosing 80 from 100

The VC dimension of convex d-gons

Number of distinct strings 'covering' all strings of same length, with restricted index selection.

All distinct k-permutations of length n, with repetitions

Counting binary sequences satisfying a certain condition

How can I deduce (3.6) from (3.5)?

$k$-out-of-$n$ combinations, arranged as matrices, satisfying certain conditions

Combinatorial proof of $ \sum_{k=0}^{n}\frac{1}{\binom{n}{k}} = \frac{n+1}{2^{n+1}}\sum_{k=0}^{n}\frac{2^{k+1}}{k+1}$

Proving that $\sum_{n=0}^r (-1)^n \binom{r}{n} (s+r-n-1)!/(s-n)! = 0$ without Taylor expansion

What is the maximal value that we can have after 99 operations?

How can I represent following series as a formula?

Proof of a combination identity: $\sum\limits_{i=0}^m\sum\limits_{j=0}^m\binom{i+j}{i}\binom{2m-i-j}{m-i}=\frac {m+1}2\binom{2m+2}{m+1}$

Combinatorics contest math question

Derangement with constraints

Proving formula sum of product of binomial coefficients

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