Combinatorics - Counting in two ways?
64803
Counting two ways, $\sum \binom{n}{k} \binom{m}{n-k} = \binom{n+m}{n}$
117349
counting triangles in a graph or its complement
9971
enumerative combinatorics,In how many ways (as a function of n) can one choose a composition α α of n
96585
Sums and permutation
69748
Semi-Ambiguous Combinatorics Problem
20221
Combinatorics - Removing Double Counted Cases
107027
Number of combinations and permutations of letters
52348
Counting the number of surjections.
149686
Combinatorics and trigonometry identity
9411
Number of permutations of $n$ elements where no number $i$ is in position $i$
57822
Number of ways to choose two disjoint subsets of a set
139039
Stars and Bars Combinatorics Problem
68882
Path to Combinatorics Problem [$1.11$]
123407
Combinatorics - binary - very interesting question
111954
Computing the cardinality of a combinatorial set
91229
Complexity of counting the number of triangles of a graph
142144
Countable or uncountable; family of disjoint triangles?