On the $(n, d)^{th}$ $f$-Ideals

Abstract

A square-free monomial ideal $I$ is called an {\it $f$-ideal}, if both $\delta_{\mathcal{F}}(I)$ and $\delta_{\mathcal{N}}(I)$ have the same $f$-vector, where $\delta_{\mathcal{F}}(I)$ ($\delta_{\mathcal{N}}(I)$, respectively) is the facet (Stanley-Reisner, respectively) complex related to $I$. In this paper, we introduce the concepts of perfect set containing $k$ and perfect set without $k$. We study the $(n, d)^{th}$ perfect sets and show that $V(n, d) \neq \emptyset$ for $d \geq 2$ and $n \geq d+2$. Then we give some algorithms to construct $(n, d)^{th}$ $f$-ideals and show an upper bound for the $(n, d)^{th}$ perfect number.