Combinatorics Summation Formula
626
Sum of combinations with varying $n$
33104
Combinatorial Proof with Summation Identity
94784
$\sum_{k=-m}^{n} \binom{m+k}{r} \binom{n-k}{s} =\binom{m+n+1}{r+s+1}$ using Counting argument
38741
Finding a general formula for summation
86900
Formula for the $1\cdot 2 + 2\cdot 3 + 3\cdot 4+\ldots + n\cdot (n+1)$ sum
10917
Give a combinatorial proof: $ n(n+1)2^{n-2} = \sum_{k=1}^{n}k^2\binom{n}{k} $
142978
combinatorics: sum of product of integer compositions
114173
Explanation of the formulas for sums $\sum nr^n$ and $\sum n^2 r^n$
65983
Combinatorial proof of binomial coefficient summation identity
155479
Summation of inner products
149010
Finding Combinations to the provided Sum value
46132
Combinatorial interpretation for the identity $\sum\limits_i\binom{m}{i}\binom{n}{j-i}=\binom{m+n}{j}$?
115433
Find the summation of given expression: $\sum_{k=1}^n k^3\binom nk$
29804
Summation with jump indices like 1,4,6,9?
98082
Another combinatorics problem: $\sum\limits_{k = 0}^n (-1)^k \binom{2n-k}k2^{2n-2k}=2n+1$
19776
Simplify a combinatorial sum
7302
$\sum k! = 1! +2! +3! + \cdots + n!$ ,is there a generic formula for this?