Number of idempotent functions $F: \{1,2,3,4,5\} \to \{1,2,3,4,5\}$
106748
Number of functions $f : A \to A$ such that $f(f(x))=f(x)$
148330
Induction Proof for $F_{2n} = F^2_{n+1} - F^2_{n-1}$
89415
Number of homomorphisms from $(\mathbb Q^+ , \,\cdot\,)$ to $(\mathbb Z_n , +)$
115298
Nested Mathematical Functions
66134
Sufficiently many idempotents and commutativity
41448
Counting set for generating functions
16687
Number of Equivalence relations of $\{1,2,3\}$
52354
Given a idempotent endomorphism, show that $M = \ker(f) \oplus \ker (f-\text{id}_M)$
5699
The number of ring homomorphisms from $\mathbb{Z}_m$ to $\mathbb{Z}_n$
73743
Number of elements in the quotient ring $\mathbb{Z}[X]/(X^2-3, 2X+4)$
150346
If $f$ is an increasing function defined on $[a,b]$ . Then, $f$ has countable number of discontinuities
31698
$f(m^2 + f(n)) = f(m)^2 + n$ for all natural numbers
146990
How to find the number of automorphisms on $\mathbb Z_2\times \mathbb Z_4$
49953
Proving that a function from $N\times N$ to $N$ is bijective.
141225
Number of all bijective functions from A to A.
20199
Find a surjective function $f:\mathbb{N}\to \mathbb{Q}$
137883
Cardinality of the set of all (real) discontinuous functions