The frequency conjecture for ratios arising from pm1+1p_{m-1}+1

Let pmp_m denote the mm-th prime, set nm=pm1+1n_m=p_{m-1}+1, and let LmL_m be the largest prime factor of nmn_m when Lm>mL_m>m; define Rm=nm/LmR_m=n_m/L_m. For a fixed positive integer rr, write φ(r)\varphi(r) for Euler's totient function. Frequency conjecture. For any fixed even integer r2r\geq 2, there is a positive constant CC close to 11 such that

#{mN:Rm=r}CNφ(r)logN.\#\{m\leq N:R_m=r\}\sim \frac{CN}{\varphi(r)\log N}.

For odd values of rr, the count is identically zero for all m3m\geq 3. The heuristic comes from requiring rpm1+1r\mid p_{m-1}+1 and the remaining quotient to be prime; the evenness restriction follows from the parity of pm1+1p_{m-1}+1. Establishing the asymptotic, including the nature of the constant CC, remains open.

Sources & referencesView supporting material

Primary source

Alexander R Povolotsky, “Frequency Ordered Ratio Families Arising from the Factorization of p_m-1+1”, arXiv:2605.08256 (2026).

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