The closed form for the number of 2-element subsets of the power set of a set with fixed overal size
42763
How to prove Vandermonde's Identity: $\sum_{k=0}^{n}\binom{R}{k}\binom{M}{n-k}=\binom{R+M}{n}$?
2900
How many $3$-subsets of $\{1,2,\ldots,10\}$ contain at least one even and one odd integer?
11849
Size of a union of two sets
79974
The cardinality of Lebesgue sets
127123
Cardinality of power set and binary sequence
132537
Class of sets of a given infinite cardinality
145214
Showing the power set is equinumerous to ${}^X2$
98850
A positional number system for enumerating fixed-size subsets?
20973
How can I find all the subsets of a set, with exactly n elements?
57644
Lower bounds for ${{2n} \choose {n}}$
55840
Number of functions from n-element set to {1, 2, …, m}
95373
Additive set function on a semiring of sets
86902
Consider the smallest number in each of the $n\choose r$ subsets (of size $r$) of $S=\{1,2,\ldots,n\}$...
142477
Closed-form expression for the number of $k$-permutations of length $n$. Duplicates allowed!
126015
Elementary number theory in sets
124060
Are these subsets of the powerset P(N) countable?
106397
Counting ways to partition a set into fixed number of subsets