Fibonacci-like partitions and their associated piecewise-defined permutations

Abstract: In this paper we introduce a family of partitions of the set of natural numbers, Fibonacci-like partitions. In particular, we introduce a Fibonacci-like partition in a number of parts corresponding to the Fibonacci numbers, the standard Fibonacci-like partitions of the first kind. That partition refines the well-known partition in two parts associated to the Wythoff sequences. In a similar way, we introduce another family of Fibonacci-like partitions of the natural numbers, with an initial segment removed, in a number of parts which also follows the Fibonacci sequence, the standard Fibonacci-like partitions of the second kind. We study some piecewise-defined permutations over Fibonacci-like partitions, which give both torsion-free and torsion elements in the symmetric group over the set of natural numbers. We give an application of Fibonacci-like partitions to the study of a sequence analyzed by A. Shapovalov and by B.J. Venkatachala. We give also a generalization of the mentioned sequence, involving techniques that are not related to Fibbonaci numbers nor Beatty sequences, obtaining an infinite family of sequences that we conjecture that produce an infinite orthogonal array in which the number of symbols, trials and factors is countable infinite, and having an automorphism group isomorphic to Z acting regularly on the symbol set.