# of invertible $n \times n$ matrices with entries in field $k$ with $q$ elements?
27865
What is the number of invertible $n\times n$ matrices in $\operatorname{GL}_n(F)$?
51770
Number of elements in a finite field extension for finite fields
97878
Are there uncountably many surjections from $\mathbb N$ to $\mathbb N$?
154581
Ring of matrices isomorphic to $O := \left\{a+b\frac{1+\sqrt{D}}{2}: a, b \in \mathbb{Z} \right\}$
89415
Number of homomorphisms from $(\mathbb Q^+ , \,\cdot\,)$ to $(\mathbb Z_n , +)$
73743
Number of elements in the quotient ring $\mathbb{Z}[X]/(X^2-3, 2X+4)$
126552
Number of subfields of finite field
107010
How many elements of order $k$ are in $S_n$?
108550
Elements of $\mathbb Q(2^{1/3})$
63007
Number of self-inverse matrices over prime field
36325
Embedding ordinals in $\mathbb{Q}$
46971
Number of surjections from $\{1,...,m\}$ to $\{1,...,n\}$
26343
Number of certain (0,1)-matrices, Stanley's Enumerative Combinatorics
96326
Number of $q$-th residues modulo $n$
139162
Complex number isomorphic to certain $2\times 2$ matrices?
25488
Let $A,B$ be $m\times m$ matrices such that $AB$ is invertible. Show $A,B$ invertible.
56898
Number of monomials of certain degree