English

$C_5$ is almost a fractalizer

Combinatorics 2026-02-17 v4

Abstract

We determine the maximum number of induced copies of a 5-cycle in a graph on nn vertices for every nn. Every extremal construction is a balanced iterated blow-up of the 5-cycle with the possible exception of the smallest level where for n=8n=8, the M\"obius ladder achieves the same number of induced 5-cycles as the blow-up of a 5-cycle on 8 vertices. This result completes work of Balogh, Hu, Lidick\'y, and Pfender [Eur. J. Comb. 52 (2016)] who proved an asymptotic version of the result. Similarly to their result, we also use the flag algebra method but we extend its use to small graphs.

Keywords

Cite

@article{arxiv.2102.06773,
  title  = {$C_5$ is almost a fractalizer},
  author = {Bernard Lidický and Connor Mattes and Florian Pfender},
  journal= {arXiv preprint arXiv:2102.06773},
  year   = {2026}
}

Comments

24 pages, minor corrections

R2 v1 2026-06-23T23:07:13.331Z