I want to write $ k = \{k1,k2,k3,...,kn\} $. How could I do this?
68215
Proper use of arbitrary number of variables
121279
Proving an Combination formula $ \binom{n}{k} = \binom{n-1}{k}+\binom{n-1}{k-1}$
73174
Prove $KN\cong K\times N$ if $K\cap N=\{e\}$
67926
$S_n$ is generated by elements of the form $(1k)$
4610
Proving an identity with a combinatorial proof: $\binom{n}{k}\binom{k}{r}=\binom{n}{r}\binom{n-r}{k-r}$
110262
Finding a closed formula for $1\cdot2\cdot3\cdots k +\dots + n(n+1)(n+2)\cdots(k+n-1)$
19571
Combinatorial proof for $\sum_{k = 0}^n \binom {r+k} k = \binom {r + n + 1} n$
103840
Calculate $\sum_{k=1}^n k2^{n-k}$
75227
If $S=\{1,2,\dots,n\}$ and $P_n(k)$ be the number of permutations of $S$ having $k$ fixed points, then $\sum_{k=0}^nk.P_{n}(k)=n!$
45204
Combinatorial proofs: having a difficult time understanding how to write them out
4555
How to write permutations as product of disjoint cycles and transpositions
32344
Let $a,k,m$ be integers. Prove that $\gcd(ka,km) = k\gcd(a,m)$.
124135
A general formula for $\sum (k-1)(k-2)(k-3)$?
120095
How many ways to split n elements in k groups?
83738
Prove $(k,n+k)=1$ iff $(k,n)=1$
44484
Combinatorial identity $i{n \choose i } =n {n-1 \choose i - 1}$
94784
$\sum_{k=-m}^{n} \binom{m+k}{r} \binom{n-k}{s} =\binom{m+n+1}{r+s+1}$ using Counting argument