On atoms and their density in the monoid of monomial ideals

We study the structure and distribution of atoms in the monoid $\mathcal{M}{\rm on}(R)$ of nonzero monomial ideals of the polynomial ring $R=K[X_1,\ldots, X_N]$, with $N\ge 2$. We characterize the atoms with at most four minimal generators and introduce the density $d(N,μ)$ of atoms among monomial i