How many possible ways can $i+j+k=n$ without taking the order into account?
65843
Number of possible combinations of x numbers that sum to y
33104
Combinatorial Proof with Summation Identity
39969
Algorithms for computing multiplicative order modulo $n$
144779
The number of ways to represent $(n^2+n)/4$ as a sum of $n/2$ distinct integers in $1,\dots,n$
120744
How many $n\times m$ binary matrices are there, up to row and column permutations?
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)
17213
what operation repeated $n$ times results in the addition operator?
74887
Combinatorial proof of the identity ${n+1\choose k+1}={k\choose k}+{k+1\choose k}+...+{n-1\choose k}+{n\choose k}$
44621
Simple binomial theorem proof: $\sum_{j=0}^{k} \binom{a+j}j = \binom{a+k+1}k$
74682
How should I solve combination addition like this?
39199
closed form for $\binom{n}{0}+\binom{n}{3}+\binom{n}{6}+...+\binom{n}{n}$
120913
How would you write a non-recursive algorithm to calculate factorials?
24212
proving how many permutations exist.
83738
Prove $(k,n+k)=1$ iff $(k,n)=1$
96585
Sums and permutation
113331
Number of ways a natural number can be written as sum of smaller natural number