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Few small primes suffice to cover unit groups
Abstract
Klurman, Shparlinski and Teräväinen showed that there is a set of at most (log Q)1+ε primes of polylogarithmic size whose subset products cover the unit group (ℤ/qℤ)× for almost all moduli q≤ Q. We show that (1/log2+o(1))log Q primes suffice, which is optimal to first order, since m primes have at most 2m subset products. The proof combines a doubling argument of Erdős--Rényi type for random subset products in a finite abelian group, modified to tolerate a small set of exceptional characters, with a one-time ``repair'' of the few primitive characters whose L-functions have zeros near s=1. An exact weighted repair gives a variant with at most (2/log2+o(1))log Q primes and an exceptional set described explicitly.
Related
BibTeX
@misc{hughes2026small,
title = {{Few small primes suffice to cover unit groups}},
author = {Scott D. Hughes},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.04678},
eprint = {2610.04678},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.04678},
}
RIS
TY - UNPB
TI - Few small primes suffice to cover unit groups
AU - Scott D. Hughes
PY - 2026
DA - 2026/10/03
PB - arXiv
DO - 10.48550/arxiv.2610.04678
UR - https://arxiv.org/abs/2610.04678
AB - Klurman, Shparlinski and Teräväinen showed that there is a set of at most (log Q)^1+ε primes of polylogarithmic size whose subset products cover the unit group (ℤ/qℤ)^× for almost all moduli q≤ Q. We show that (1/log2+o(1))log Q primes suffice, which is optimal to first order, since m primes have at most 2^m subset products. The proof combines a doubling argument of Erdős--Rényi type for random subset products in a finite abelian group, modified to tolerate a small set of exceptional characters, with a one-time ``repair'' of the few primitive characters whose L-functions have zeros near s=1. An exact weighted repair gives a variant with at most (2/log2+o(1))log Q primes and an exceptional set described explicitly.
ER -