Combinatorial Identity, difficult
115686
A finite summation of double binomial coefficients
146867
Combinatorial Proof Of A Number Theory Theorem--Confusion
69748
Semi-Ambiguous Combinatorics Problem
81729
Combinatorial proof of $\sum_{k=0}^{n}(-1)^{k}\binom{n}{k}(l-k)^n=n!$, using inclusion-exclusion
19571
Combinatorial proof for $\sum_{k = 0}^n \binom {r+k} k = \binom {r + n + 1} n$
145524
Proving this identity $\sum_k\frac{1}{k}\binom{2k-2}{k-1}\binom{2n-2k+1}{n-k}=\binom{2n}{n-1}$ using lattice paths
25826
Proof of a combinatorial identity: $\sum\limits_{i=0}^n {2i \choose i}{2(n-i)\choose n-i} = 4^n$
144571
A conjecture including binomial coefficients
8458
Combinatorics problem based on Ferrers graph
105237
Alternating sum of binomial coefficients identity
33104
Combinatorial Proof with Summation Identity
46132
Combinatorial interpretation for the identity $\sum\limits_i\binom{m}{i}\binom{n}{j-i}=\binom{m+n}{j}$?
36388
How to derive this Combinatorial identity
87320
Proving identities like $\sum_{k=1}^nk{n\choose k}^2=n{2n-1\choose n}$ combinatorially
15349
Combinatorics riddle: keys and a safe
114522
Prove that identity is unique in a group
1139
Combinatorial proof of $\sum_{j=0}^{k} \binom{n}{j} = \sum_{j=0}^k \binom{n-1-j}{k-j}2^j$