Transcendence of Values of the Iterated Exponential Function at Algebraic Points

Hirotaka Kobayashi, Kota Saito, Wataru Takeda

Research output: Contribution to journalArticlepeer-review

Abstract

We say that the limit of a sequence of functions x, xx, xxx, … is the iterated exponential function, denoted by h(x). By a result of Barrow, this limit is convergent for every (formula presented). In this paper, we prove that, for each fixed integer k ≥ 2, the limit h(A) is transcendental for all but finitely many algebraic numbers (formula presented). Furthermore, let Q(k) be the cardinality of exceptional points A. We prove that the ratio Q(k)/ϕ(k) approaches e − 1/e as k → ∞, where ϕ(k) denotes Euler’s totient function.

Original languageEnglish
Article number23.3.3
JournalJournal of Integer Sequences
Volume26
Issue number3
Publication statusPublished - 2023
Externally publishedYes

Keywords

  • Gelfond-Schneider theorem
  • iterated exponential
  • Lindemann theorem
  • transcendental number

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