number of $k$-subsets of an $n$ element set, where $k \equiv 1 \bmod 3$
135698
Count subsets whose cardinalities are congruent to 0, 1 and 2 modulo 3 respectively
15000
Show that number of elements in $(Z/nZ)^*$ is $\phi (n)$
7938
Number of Homomorphisms from $\Bbb{Z}_m$ to $\Bbb{Z}_n$
86902
Consider the smallest number in each of the $n\choose r$ subsets (of size $r$) of $S=\{1,2,\ldots,n\}$...
136306
Let $A$ be a finite set and let $B$ be a subset of $A$ with $|A|=n$,$|B|=m$ and $0<m<n$. Count the subsets of $A$ containing $ B.$
21754
Partition a set into subsets of size $k$
108275
How do I count the subsets of a set whose number of elements is divisible by 3? 4?
70761
Number of ways to connect sets of $k$ dots in a perfect $n$-gon
113668
Uncountable chain of subsets of $\mathbb N$
141984
Find the number of homomorphisms between $\mathbb{Z}_m$ and $\mathbb{Z}_n$
83115
A set of elements in a reduced unity ring
59535
Prove that there exists such a set of $n$ positive integers
35362
Number of equivalence relations on a set
16687
Number of Equivalence relations of $\{1,2,3\}$
107010
How many elements of order $k$ are in $S_n$?
111954
Computing the cardinality of a combinatorial set
45448
Minimum number of $k$-partitions of a set of size $n$ to enumerate all $n \choose k$ combinations