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For questions on divisors and multiples, mainly but not exclusively of integers, and related and derived notions such as sums of divisors, perfect numbers and so on.

6 votes
Accepted

Smallest integer not divisible by integers in a finite set

Given an integer $n$, the Jacobsthal function $g(n)$ is the least integer, so that among any $g(n)$ consecutive integers $a,a+1,\dots,a+g(n)-1$ there is at least one that is coprime to $n$. Let $\nu(n …
Gjergji Zaimi's user avatar
10 votes
Accepted

Large gaps between consecutive irreducible polynomials with small heights

At the cost of having the degree be very large you can always choose a $k$-gap with coefficients in $\lbrace 0,1\rbrace$. Pick a large $n$ so that $n\equiv -j\pmod{p_j}$, for all $1\le j\le k$. Where …
Gjergji Zaimi's user avatar
5 votes
Accepted

Trying to prove a congruence for Stirling numbers of the second kind

Here is a quick generating function argument. Start with the following lemma Lemma: The power series $$\frac{1}{(1-x)(1-2x)\cdots (1-kx)}$$ is even $\pmod{k+1}$ when $k+1$ is odd, and even $\pmo …
Gjergji Zaimi's user avatar
4 votes
Accepted

Sum of divisors and unitary divisors as the eigenvalue and the spectral norm of some additio...

In both cases you are really only using the additive structure of your rings, so this is really a question about abelian groups. Assuming $n = p_1^{a_1} \cdots p_r^{a_r}$, when studying $A_n$ we are w …
Gjergji Zaimi's user avatar