English

Packing arithmetic progressions

Combinatorics 2026-03-04 v1

Abstract

Let F={A1,A2,,Ak}\mathcal{F}=\{A_1,A_2,\ldots,A_k\} be a collection of finite arithmetic progressions, where each AdA_d is an initial segment of the set Dd={d,2d,3d,}D_d=\{d,2d,3d,\ldots\} of consecutive multiples of a positive integer dd. Let m(F)m(\mathcal{F}) denote the minimum length of an interval containing pairwise disjoint \emph{shifted} copies of all members of the family F\mathcal{F}. We study this parameter in the following two cases: for a fixed positive integer nn, (1) each progression in F\mathcal{F} has the form Ad=Dd{1,2,,n}A_d=D_d\cap\{1,2,\ldots,n\}, and (2) all progressions AdA_d of F\mathcal{F} have the same size nn, that is, Ad=Dd{1,2,,nd}A_d=D_d\cap \{1,2,\ldots, nd\}. We in particular derive the following asymptotic estimates. In case (1), when k=nk=n, we get m(F)=Θ(n3/2/lnn)m(\mathcal{F})=\Theta(n^{3/2}/\ln n). In case (2), when k=nk=n, we get m(F)=Θ(n3/lnn)m(\mathcal{F})=\Theta(n^3/\ln n), while if k>k0(n)k>k_0(n), then m(F)<3knm(\mathcal{F}) < 3kn. In both cases we additionally determine m(F)m(\mathcal{F}) asymptotically or settle its order of magnitude for all k<nk<n.

Keywords

Cite

@article{arxiv.2603.02786,
  title  = {Packing arithmetic progressions},
  author = {Noga Alon and Michał Dębski and Jarosław Grytczuk and Jakub Przybyło},
  journal= {arXiv preprint arXiv:2603.02786},
  year   = {2026}
}
R2 v1 2026-07-01T11:00:43.502Z