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(Non)Automaticity of number theoretic functions

Michael Coons (2010)

Journal de Théorie des Nombres de Bordeaux

Denote by λ ( n ) Liouville’s function concerning the parity of the number of prime divisors of n . Using a theorem of Allouche, Mendès France, and Peyrière and many classical results from the theory of the distribution of prime numbers, we prove that λ ( n ) is not k –automatic for any k > 2 . This yields that n = 1 λ ( n ) X n 𝔽 p [ [ X ] ] is transcendental over 𝔽 p ( X ) for any prime p > 2 . Similar results are proven (or reproven) for many common number–theoretic functions, including ϕ , μ , Ω , ω , ρ , and others.

On consecutive integers divisible by the number of their divisors

Titu Andreescu, Florian Luca, M. Tip Phaovibul (2016)

Acta Arithmetica

We prove that there are no strings of three consecutive integers each divisible by the number of its divisors, and we give an estimate for the number of positive integers n ≤ x such that each of n and n + 1 is a multiple of the number of its divisors.

On rough and smooth neighbors.

William D. Banks, Florian Luca, Igor E. Shparlinski (2007)

Revista Matemática Complutense

We study the behavior of the arithmetic functions defined byF(n) = P+(n) / P-(n+1) and G(n) = P+(n+1) / P-(n) (n ≥ 1)where P+(k) and P-(k) denote the largest and the smallest prime factors, respectively, of the positive integer k.

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