## Abstract

It has been conjectured that every Steiner triple system of order v 6= 7 has chromatic index at most (v + 3)=2 when v = 3 (mod 6) and at most (v + 5)=2 when v = 1 (mod 6). Herein, we construct a Steiner triple system of order v with chromatic index at least (v + 3)=2 for each integer v = 3 (mod 6) such that v ≥ 15, with four possible exceptions. We further show that the maximum number of disjoint parallel classes in the systems constructed is sublinear in v. Finally, we establish for each order v ≥ 15 (mod 18) that there are at least vv^{2}(1=6+o(1)) nonisomorphic Steiner triple systems with chromatic index at least (v + 3)=2 and that some of these systems are cyclic.

Original language | English |
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Pages (from-to) | 2603-2611 |

Number of pages | 9 |

Journal | SIAM Journal on Discrete Mathematics |

Volume | 31 |

Issue number | 4 |

DOIs | |

Publication status | Published - 2017 |

## Keywords

- Block coloring
- Chromatic index
- Parallel class
- Steiner triple system