Colored compositions, Invert operator and elegant compositions with the "black tie"

TL;DR

This paper explores the relationship between colored compositions of integers and the Invert operator, introducing new methods and interpretations that connect combinatorics with classical number sequences and operators.

Contribution

It establishes a novel connection between colored compositions and the Invert operator, providing new combinatorial proofs, formulas, and interpretations for these mathematical objects.

Findings

Connected colored compositions with the Invert operator.

Derived a simple criterion for counting colored compositions.

Provided new interpretations for convolution operator.

Abstract

This paper shows how the study of colored compositions of integers reveals some unexpected and original connection with the Invert operator. The Invert operator becomes an important tool to solve the problem of directly counting the number of colored compositions for any coloration. The interesting consequences arising from this relationship also give an immediate and simple criterion to determine whether a sequence of integers counts the number of some colored compositions. Applications to Catalan and Fibonacci numbers naturally emerge, allowing to clearly answer to some open questions. Moreover, the definition of colored compositions with the "black tie" provides straightforward combinatorial proofs to a new identity involving multinomial coefficients and to a new closed formula for the Invert operator. Finally, colored compositions with the "black tie" give rise to a new combinatorial interpretation for the convolution operator, and to a new and easy method to count the number of parts of colored compositions.