# Tagged Questions

Questions on congruences, linear diophantine equations, greatest common divisor, divisibility, etc.

570 views

79 views

### Is there a finite list of identites in the language of $(\mathbb{N},0,1,+,\times,\mathrm{gcd},\mathrm{lcm})$ that generates all the others?

Let $\Phi$ denote the set of all identities satisfied by $(\mathbb{N},0,1,+,\times,\mathrm{gcd},\mathrm{lcm}).$ Question. Is $\Phi$ finitely axiomatizable? If so, I'd like to see a list of ...
71 views

### Making perfect cube from factors of $20!$

At least how many different factors of $20!$ must we choose so that we can always find some subset whose product is a perfect cube? For example, if we choose $\{2,3,5,7,11,13,17,19,22,26,34,38\}$, ...
62 views

### The Greatest Common Divisor of All Numbers of the Form $n^a-n^b$

For fixed nonnegative integers $a$ and $b$ such that $a>b$, let $$g(a,b):=\underset{n\in\mathbb{Z}}{\gcd}\,\left(n^a-n^b\right)\,.$$ Here, $0^0$ is defined to be $1$. (Technically, we can also ...
Given a (not strictly) decreasing sequence of natural positive numbers $a_1, a_2, \dots, a_n$ prove that $$\prod_{i<j} j-i \quad\big|\quad \prod_{i<j} a_i - a_j - i +j$$ I already know a ...
Consider the following sequence of operations : Start with a natural number $n$ and then round it up to the closest multiple of $n-1$ .Then round up this new number to the closest multiple of \$n-...