Can an explicit formula be found for a bijection $f \colon \mathbb{N} \to \mathbb{Q}$?
5803
Produce an explicit bijection between rationals and naturals?
152297
Understanding quotients of $\mathbb{Q}[x]$
145875
Inverse of a bijection f is equal to its derivative
100134
Proving existence of a surjection $2^{\aleph_0} \to \aleph_1$ without AC
119549
Prove the even integers are countable (by explicitly giving a bijection $\mathbb{N} \to E$)
64583
Number of surjective functions from A to B
36325
Embedding ordinals in $\mathbb{Q}$
5375
Is there a bijective function mapping Natural numbers to Natural numbers, other than $f(n) = n$?
41895
Show $\text{Hom}_{Ab}(A,\mathbb{Q}) = \{0\}$ for finite $A$
107098
Find an explicit formula for the recurrence $a_n = n(a_{n-1} + a_{n-2})$ knowing that $ a_0=1$ and $a_1=2$.
63478
Is $\mathbb{Q}(\sqrt{2}) \cong \mathbb{Q}(\sqrt{3})$?
120699
Is $\mathcal{O}_{\mathbb{Q}(\sqrt{5})} = \mathbb{Z}[\phi]$?
38242
Explicit bijection between the successor of $\alpha$ and $\alpha$ (infinite ordinal).
31391
bijection between $\mathbb{N}$ and $\mathbb{N}\times\mathbb{N}$
117793
Finding a function $\mathbb{N} \to \mathbb{N}$ that is surjective but not injective.
93964
Proving that $f$ is a bijection from $N$x$N$ to $N$.
46971
Number of surjections from $\{1,...,m\}$ to $\{1,...,n\}$