The M\"obius function of the poset of triangular numbers under divisibility

Abstract

This paper analyzes the M\"obius ($\mu(i)$) function defined on the partially ordered set of triangular numbers ($\mathcal T(i)$) under the divisibility relation. We make conjectures on the asymptotic behavior of the classical M\"obius and Mertens functions based on experimental data and other proven conjectures. We first introduce the growth of partial sums of $\mu_{\mathcal T}(i)$ and analyze how the growth is different from the classical M\"obius function, and then analyze the relation between the partial sums of $|\mu_{\mathcal T}(i)|$, and how it is similar to the asymptotic classical M\"obius function. Which also happens to involve the Riemann zeta function. Then we create Hasse diagrams of the poset, this helps introduce a method to visualize the divisibility relation of triangular numbers. This also serves as a basis for the zeta and M\"obius matrices. Looking specifically into the poset defined by $(\mathbb{N}, \leq_{\mathcal T})$, or triangular numbers under divisibility and applying the M\"obius function to it, we can create our desired matrices. And then using Python libraries we create visualizations for further analysis and can project previously mentioned patterns. Through this, we can introduce two more novel conjectures bounding $\mu_{\mathcal T}(n)$ and the sums of $\frac{\mu_{\mathcal T}}{i}$. We conclude the paper with divisibility patterns in the Appendix, with proofs of the helpful and necessary propositions.