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Recently, Harrington et al. [‘Every arithmetic progression contains infinitely many b-Niven numbers’, Bull. Aust. Math. Soc.109(3) (2024), 409–413] proved that every arithmetic progression contains infinitely many base-b Niven numbers for any fixed $b\ge 2$. We use a sparse repunit construction to treat a structured two-base version of the same problem, showing that every arithmetic progression with common difference relatively prime to b contains infinitely many integers that are simultaneously b-Niven and $b^k$-Niven (indeed, we can obtain simultaneous $b^\ell $-Niven-ness for $\ell =1,\ldots , k$).
A Lehmer number is a composite positive integer n such that ϕ(n)|n − 1. In this paper, we show that given a positive integer g > 1 there are at most finitely many Lehmer numbers which are repunits in base g and they are all effectively computable. Our method is effective and we illustrate it by showing that there is no such Lehmer number when g ∈ [2, 1000].
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