English

Intersecting integer partitions

Combinatorics 2013-04-25 v1

Abstract

If a1,a2,...,aka_1, a_2, ..., a_k and nn are positive integers such that n=a1+a2+...+akn = a_1 + a_2 + ... + a_k, then the sum a1+a2+...+aka_1 + a_2 + ... + a_k is said to be a \emph{partition of nn} of \emph{length kk}, and a1,a2,...,aka_1, a_2, ..., a_k are said to be the \emph{parts} of the partition. Two partitions that differ only in the order of their parts are considered to be the same. We say that two partitions \emph{intersect} if they have at least one common part. We call a set AA of partitions \emph{intersecting} if any two partitions in AA intersect. Let Pn,kP_{n,k} be the set of all partitions of nn of length kk. We conjecture that if 2kn2 \leq k \leq n, then the size of any intersecting subset of Pn,kP_{n,k} is at most the size of Pn1,k1P_{n-1,k-1}, which is the size of the intersecting subset of Pn,kP_{n,k} consisting of those partitions which have 1 as a part. The conjecture is trivially true for n2kn \leq 2k, and we prove it for n5k5n \geq 5k^5. We also generalise this for subsets of Pn,kP_{n,k} with the property that any two of their members have at least tt common parts.

Keywords

Cite

@article{arxiv.1304.6563,
  title  = {Intersecting integer partitions},
  author = {Peter Borg},
  journal= {arXiv preprint arXiv:1304.6563},
  year   = {2013}
}

Comments

8 pages, submitted

R2 v1 2026-06-22T00:05:28.115Z