English

Variants on Andrica's conjecture with and without the Riemann hypothesis

Number Theory 2025-04-29 v3

Abstract

The gap between what we can explicitly prove regarding the distribution of primes and what we suspect regarding the distribution of primes is enormous. It is (reasonably) well-known that the Riemann hypothesis is not sufficient to prove Andrica's conjecture: n1\forall n\geq 1, is pn+1pn1\sqrt{p_{n+1}}-\sqrt{p_n} \leq 1? But can one at least get tolerably close? I shall first show that with a logarithmic modification, provided one assumes the Riemann hypothesis, one has pn+1lnpn+1pnlnpn<1125;(n1). {\sqrt{p_{n+1}}\over\ln p_{n+1}} -{\sqrt{p_n}\over\ln p_n} < {11\over25}; \qquad (n\geq1). Then, by considering more general mthm^{th} roots, again assuming the Riemann hypothesis, I shall show that pn+1mpnm<4425e(m2);(n3;  m>2). {\sqrt[m]{p_{n+1}}} -{\sqrt[m]{p_n}} < {44\over25 \,e\, (m-2)}; \qquad (n\geq 3;\; m >2). In counterpoint, if we limit ourselves to what we can currently prove unconditionally, then the only explicit Andrica-like results seem to be variants on the results below: ln2pn+1ln2pn<9;(n1). \ln^2 p_{n+1} - \ln^2 p_n < 9; \qquad (n\geq1). ln3pn+1ln3pn<52;(n1). \ln^3 p_{n+1} - \ln^3 p_n < 52; \qquad (n\geq1). ln4pn+1ln4pn<991;(n1). \ln^4 p_{n+1} - \ln^4 p_n < 991; \qquad (n\geq1). I shall also slightly update the region on which Andrica's conjecture is unconditionally verified.

Keywords

Cite

@article{arxiv.1804.02500,
  title  = {Variants on Andrica's conjecture with and without the Riemann hypothesis},
  author = {Matt Visser},
  journal= {arXiv preprint arXiv:1804.02500},
  year   = {2025}
}

Comments

V1: 12 pages; V2: 9 pages. Discussion simplified and streamlined. Various numerical constants improved. Extra section added on what can be proved unconditionally. Updated discussion on using maximal prime gaps to verify the standard Andrica conjecture up to 1.8 x 10^{19}. V3: 10 pages; 4 references added; some cosmetic changes; more discussion of numerics; closely resembles published version