Discrete mathematics, counting two ways
42763
How to prove Vandermonde's Identity: $\sum_{k=0}^{n}\binom{R}{k}\binom{M}{n-k}=\binom{R+M}{n}$?
96585
Sums and permutation
9411
Number of permutations of $n$ elements where no number $i$ is in position $i$
24212
proving how many permutations exist.
91229
Complexity of counting the number of triangles of a graph
107964
Simple combinatorics problem.
125132
How can I (algorithmically) count the number of ways n m-sided dice can add up to a given number?
126025
Computing the inverse of a permutation
20174
Discrete mathematics bit strings
30136
Proof that a Combination is an integer
39724
Combinatorial Identities
132921
Counting problem, number of moves
57822
Number of ways to choose two disjoint subsets of a set
20221
Combinatorics - Removing Double Counted Cases
41448
Counting set for generating functions
3479
How to count the no. of distinct ways in which $1,2,...,6$ can be assigned to $6$ faces of a cube?
140433
The number of ways of writing an integer as a sum of two squares