A cellular automaton on a torus.
Menon’s identity is a classical identity involving gcd sums and the Euler totient function . A natural generalization of is the Klee’s function . We derive a Menon-type identity using Klee’s function and a generalization of the gcd function. This identity generalizes an identity given by Y. Li and D. Kim (2017).
We examine primitive roots modulo the Fermat number . We show that an odd integer is a Fermat prime if and only if the set of primitive roots modulo is equal to the set of quadratic non-residues modulo . This result is extended to primitive roots modulo twice a Fermat number.
In the paper we discuss the following type congruences: where is a prime, , , and are various positive integers with , and . Given positive integers and , denote by the set of all primes such that the above congruence holds for every pair of integers . Using Ljunggren’s and Jacobsthal’s type congruences, we establish several characterizations of sets and inclusion relations between them for various values and . In particular, we prove that for all , and , and for...