Journal of Integer Sequences, Vol. 24 (2021), Article 21.5.5

On Almost Lehmer Numbers

Tomohiro Yamada
Center for Japanese Language and Culture
Osaka University
562-8558, 8-1-1, Aomatanihigashi
Minoo, Osaka


We consider composite numbers n such that φ(n) divides (n– 1) for some squarefree divisor of n – 1. We discuss two cases, according to whether the number of prime factors of is bounded or not. We give a few instances and upper bounds for the number of such integers below a given number.

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(Concerned with sequences A001055 A020555 A033833 A173703 A337316 A338998.)

Received November 24 2020; revised versions received November 25 2020; February 25 2021. Published in Journal of Integer Sequences, April 25 2021.

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