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The Fibonacci numbers are not an additive uniqueness set for multiplicative functions
Abstract
Let (Fn)n≥ 0 be the Fibonacci sequence. We show that a multiplicative function f satisfying f(Fn+Fm)=f(Fn)+f(Fm) (n,m≥ 1) need not be the identity function, even when f takes positive integer values. This answers negatively a question posed by Spiro in 1992. The smallest example presented here is obtained from F31=557· 2417. We prove the required divisibility equivalence, formulate an abstract prime-signature construction, and give a practical criterion producing further examples. We also describe the AI-assisted search that led to the construction and provide a reproducible certificate checker.
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BibTeX
@misc{park2026fibonacci,
title = {{The Fibonacci numbers are not an additive uniqueness set for multiplicative functions}},
author = {Poo-Sung Park},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.08137},
eprint = {2609.08137},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.08137},
}
RIS
TY - UNPB
TI - The Fibonacci numbers are not an additive uniqueness set for multiplicative functions
AU - Poo-Sung Park
PY - 2026
DA - 2026/09/08
PB - arXiv
DO - 10.48550/arxiv.2609.08137
UR - https://arxiv.org/abs/2609.08137
AB - Let (F_n)_n≥ 0 be the Fibonacci sequence. We show that a multiplicative function f satisfying f(F_n+F_m)=f(F_n)+f(F_m) (n,m≥ 1) need not be the identity function, even when f takes positive integer values. This answers negatively a question posed by Spiro in 1992. The smallest example presented here is obtained from F_31=557· 2417. We prove the required divisibility equivalence, formulate an abstract prime-signature construction, and give a practical criterion producing further examples. We also describe the AI-assisted search that led to the construction and provide a reproducible certificate checker.
ER -