The density conjecture for prime divisors absent from the rr-derangement numbers

For a fixed positive integer rr, let Cr(n)C_r(n) denote the rr-derangement numbers, and let P\mathbb{P} be the set of prime numbers. Define

Ar:={pP:nr pCr(n)}.\mathcal{A}_r:=\{p\in\mathbb{P}:\forall_{n\geq r}\ p\nmid C_r(n)\}.

Density conjecture. The set Ar\mathcal{A}_r is infinite. Moreover,

limn+(Ar{1,...,n})(P{1,...,n})=1e.\lim_{n\rightarrow +\infty} \frac{\sharp (\mathcal{A}_r\cap\{1,...,n\})}{\sharp (\mathbb{P}\cap\{1,...,n\})} = \frac{1}{e}.

The preceding result establishes that the complementary set of primes dividing at least one number Cr(n)C_r(n) is infinite. The asserted infinitude and natural density 1/e1/e of the primes that divide none of the rr-derangement numbers remain unproved in the supplied text.

Sources & referencesView supporting material

Primary source

Chenying Wang, Piotr Miska and István Mező, “The r-derangement numbers”, arXiv:1803.04529 (2018).

Progress summary

Never refreshed

Nothing recorded yet. Refresh searches the literature and the public web for attempts on this problem, and writes the first summary here.

Solutions 0

No solutions have been posted yet.