number of surjective function from a set [k] to [n]
61
Calculating the total number of surjective functions
82207
Number of Pairs of Subsets
57221
counting the number of elements in a conjugacy class of $S_n$
74453
Injective and Surjective Functions
52348
Counting the number of surjections.
45792
Rigorous proof that surjectivity implies injectivity for finite sets
106748
Number of functions $f : A \to A$ such that $f(f(x))=f(x)$
102515
Counting functions between two sets
85658
Number of onto functions
141225
Number of all bijective functions from A to A.
1643
Number of reflexive relations defined on a set A with n elements
109710
Bijection between $\mathbb N \times \mathbb N$ and $\mathbb N$
107010
How many elements of order $k$ are in $S_n$?
104274
Express $C$ interms of the sets $A_n$
67451
Building a bijection from a finite union of countable sets to $\mathbb{N}$
115973
Computing the number of nonisomorphic finite abelian groups of order $n$
45448
Minimum number of $k$-partitions of a set of size $n$ to enumerate all $n \choose k$ combinations