Insight into $\pmod {2^n \pm 1}$
3128
Why $9$ & $11$ are special in divisibility tests using decimal digit sums? (casting out nines & elevens)
23153
$\bmod p\!:\ x^2\equiv 1\iff x\equiv \pm1\ $ for prime $p$
57654
Congruent Modulo $n$: definition
151636
Fast way to calculate n! mod m where m is prime?
112390
Solutions of $x^2 \equiv 1 \pmod N$
29578
Why is $\binom{2n}{n} \asymp \Theta \big(\frac{2^{2n}}{\sqrt{n}}\big)$?
135986
Show if $a \equiv b \pmod{m}$ then $ac \equiv bc\pmod{mc}$
102398
Help deriving that $\mathrm{sign} : S_n\to \{\pm 1\}$ is multiplicative
34323
Prove that $a^{(p-1)/2} \equiv 1$ (mod p) and $a^{(p-1)/2} \equiv -1 \pmod p$
141369
If $a+b\equiv0\pmod m$ and $c+d\equiv 0\pmod m$ then $ac\equiv bd\pmod m$. Demonstration.
30630
Proving ${n \choose p} \equiv \Bigl[\frac{n}{p}\Bigr] \ (\text{mod} \ p)$
143754
Finding the solution of the congruence $4x\equiv16\pmod{26}$
2218
Prove that $(n-1)! \equiv -1 \pmod{n}$ iff $n$ is prime [Wilson's Theorem]
22029
Solving modular arithmetic questions
24572
Does $n \mid 2^{2^n+1}+1$ imply $n \mid 2^{2^{2^n+1}+1}+1$?
41925
What is the distribution of primes modulo $n$?
153862
A question about a primitive root mod $p=2^{2^k}+1$, where $p$ is prime.