English

Partitions enumerated by self-similar sequences

Combinatorics 2023-03-22 v1 Number Theory

Abstract

The Fibonacci numbers are the prototypical example of a recursive sequence, but grow too quickly to enumerate sets of integer partitions. The same is true for the other classical sequences a(n)a(n) defined by Fibonacci-like recursions: the tribonacci, Padovan, Pell, Narayana's cows, and Lucas sequences. For each sequence a(n)a(n), however, we can define a related sequence sa(n)\textrm{sa}(n) by defining sa(n)\textrm{sa}(n) to have the same recurrence and initial conditions as a(n)a(n), except that sa(2n)=sa(n)\textrm{sa}(2n)=\textrm{sa}(n). Growth is no longer a problem: for each nn we construct recursively a set SA(n)\mathcal{SA}(n) of partitions of nn such that the cardinality of SA(n)\mathcal{SA}(n) is sa(n)\textrm{sa}(n). We study the properties of partitions in SA(n)\mathcal{SA}(n) and in each case we give non-recursive descriptions. We find congruences for sa(n)\textrm{sa}(n) and also for psa(n)\textrm{psa}(n), the total number of parts in all partitions in SA(n)\mathcal{SA}(n).

Keywords

Cite

@article{arxiv.2303.11493,
  title  = {Partitions enumerated by self-similar sequences},
  author = {Cristina Ballantine and George Beck},
  journal= {arXiv preprint arXiv:2303.11493},
  year   = {2023}
}

Comments

36 pages

R2 v1 2026-06-28T09:25:16.087Z