So's Conjecture for Integral Circulant Graphs of Order p^aq
Abstract
So conjectured that, for a fixed positive integer n, the ordinary adjacency spectrum of an integral circulant graph of order n determines its divisor set. We prove this for graphs of order p to the power a times q, where p and q are primes with p less than q and a is at least one. To handle coincident eigenvalues arising from distinct greatest-common-divisor classes, we use a spectral counting measure. For connected graphs, an exact identity recovers the part of the divisor set consisting of one and q, when present, together with the counting measure for a graph of order p to the power a minus one times q. Strong induction and decomposition into connected components then recover the full divisor set, including the case p equals two and disconnected graphs.
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BibTeX
@misc{jiang2026conjecture,
title = {{So's Conjecture for Integral Circulant Graphs of Order p^aq}},
author = {Jianwei Jiang and Chunhua Yang},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.20072},
eprint = {2609.20072},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.20072},
}
RIS
TY - UNPB
TI - So's Conjecture for Integral Circulant Graphs of Order p^aq
AU - Jianwei Jiang
AU - Chunhua Yang
PY - 2026
DA - 2026/09/17
PB - arXiv
DO - 10.48550/arxiv.2609.20072
UR - https://arxiv.org/abs/2609.20072
AB - So conjectured that, for a fixed positive integer n, the ordinary adjacency spectrum of an integral circulant graph of order n determines its divisor set. We prove this for graphs of order p to the power a times q, where p and q are primes with p less than q and a is at least one. To handle coincident eigenvalues arising from distinct greatest-common-divisor classes, we use a spectral counting measure. For connected graphs, an exact identity recovers the part of the divisor set consisting of one and q, when present, together with the counting measure for a graph of order p to the power a minus one times q. Strong induction and decomposition into connected components then recover the full divisor set, including the case p equals two and disconnected graphs.
ER -