New posts in Elementary Number Theory

Show that $\sum_{k=1}^{a-1}(k,a)\equiv0\pmod{a-1}\iff a $ is prime

The $2019$th strictly positive integer $n$ such that $\binom{2n}{n}$ is not divisible by $5$

Prove there are infinitely many squares ending in the digits $54321$

How to prove that a hexagon is the regular polygon with the most sides that can tile a plane

For different integers there exists an integer so that exactly one of the sums is prime.

Explain the solution to USAMO $1991/\rm P3$

Divisors of n! including 1 which sum to n!

Does every number divide some $n^2+1$?

Is there a positive integer $n$ such that the prime divisors of $n^3 - 1$ are $2$, $3$ and $7$?

What are all the integral solutions of $n!=m(m^2-1)$?