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Rigidity of Averages over the Two Largest Prime Factors
Abstract
Let P1(n) and P2(n) be the largest and second-largest distinct prime factors of n. Alladi and Johnson asked whether there is a bounded function f on the primes such that the averages 1/x∑2≤ n≤ xf(P1(n)) and 1/x∑2≤ n≤ xf(P2(n)) converge to different limits, where f(P2(n))=0 when n is a prime power. We show that this cannot happen. In fact, whenever the first average converges, the second also converges to the same limit.
Related
BibTeX
@misc{chen2026rigidity,
title = {{Rigidity of Averages over the Two Largest Prime Factors}},
author = {Dijia Chen},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2608.05191},
eprint = {2608.05191},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2608.05191},
}
RIS
TY - UNPB
TI - Rigidity of Averages over the Two Largest Prime Factors
AU - Dijia Chen
PY - 2026
DA - 2026/10/26
PB - arXiv
DO - 10.48550/arxiv.2608.05191
UR - https://arxiv.org/abs/2608.05191
AB - Let P_1(n) and P_2(n) be the largest and second-largest distinct prime factors of n. Alladi and Johnson asked whether there is a bounded function f on the primes such that the averages 1/x∑_2≤ n≤ xf(P_1(n)) and 1/x∑_2≤ n≤ xf(P_2(n)) converge to different limits, where f(P_2(n))=0 when n is a prime power. We show that this cannot happen. In fact, whenever the first average converges, the second also converges to the same limit.
ER -