How to compute this combinatoric sum?
54442
Sum of $k {n \choose k}$ is $n2^{n-1}$
65983
Combinatorial proof of binomial coefficient summation identity
142978
combinatorics: sum of product of integer compositions
147766
Sum of Permutations from 0 to n
28027
Find $\sum_{k=0}^{n}4^k \binom{n}{k}$
134599
How do I do Combinatorics / Counting?
61270
Binomial Theorem Sum
45204
Combinatorial proofs: having a difficult time understanding how to write them out
140877
Evaluate the sum $\sum_{k=1}^n {n \choose k-1} {n \choose k}$
148949
Find the value of $\sum_{k=1}^{n} k \binom {n} {k}$
71797
Combinatorial argument for $\sum\limits_{k=i}^{n}\binom{n}{k}\binom{k}{i} = \binom{n}{i}2^{n-i}$
142303
Alternating sum of binomial coefficients multiplied by (1/k+1)
151085
Simplify the sum $ \sum_{i=0}^{k}(-1)^i i \binom{n}{i} \binom{n}{k-i}$
60860
Combinatorial proof of $\sum_{i = 0}^{n} \binom{i}{r - 1} = \binom{n + 1}{r}$ and then use result to find a formula for $1^2 + 2^2 + \ldots + n^2$
130083
Evaluating sum of a combination series
27141
Combinatorics identity question
149010
Finding Combinations to the provided Sum value