Kimberling's linear complementary equations: automatic structure and exact bounds
In 2018 Kimberling added to the On-Line Encyclopedia of Integer Sequences the solutions of complementary equations such as a(n) = 2b(n−1) − b(n−2) + 2n, where a(0) = 1, a(1) = 2, b(0) = 3, b(1) = 4, and b is the increasing sequence of positive integers not in a. For 21 of these sequences he conjectured bounds of the form L < x(n) − ρn < U for n ≥ 1, where ρ is the growth constant of x. The 11 equations behind these conjectures have the form a(n) = 2b(n−s) − b(n−s−1) + kn + c with s ∈ {0,1} and k ∈ {2,3,4}. For each of them we show that a(n) − (k+1)n and b(n) − n are sums of an explicit shift function and an automatic sequence in the Ostrowski numeration system of [0; k, k, k, …], and we verify this with the Walnut prover. From this we compute the exact infimum and supremum of x(n) − ρn for all 22 sequences; they lie in Q(√(k²+4)). Twenty of the 21 conjectures are true, three of them after a misprint is corrected. The conjecture for A297836 is false: it fails at n = 2 and for infinitely many n. We also prove a conjecture of Kimberling and Moses (2019) on three sequences defined by a mex rule, by showing that the first of them is ⌊(1+√2)n + 1 + √2/2⌋.
Authors
- Alex Ashburn (ORCID: https://orcid.org/0009-0007-4343-959X)
Publication Details
- Journal
- Zenodo (CERN European Organization for Nuclear Research)
- Published
- 2026-10-03
- DOI
- https://doi.org/10.5281/zenodo.23125012
- Primary Topic
- semigroups and automata theory
- Type
- preprint