# name
Alternating Catalan numbers and cover with triple ramification

# metadata.dc.description.abstract[].value
The Catalan numbers $C_n:=\frac{1}{n+1}\left(\begin{array}{c}2 n \\ n\end{array}\right)$ form one of the most ubiquitous sequence in classical combinatorics. Stanley's book [St] lists 66 different manifestations of these numbers in various counting problems. In the theory of algebraic curves, the Catalan number $C_n$ counts the covers $C \rightarrow \mathbb{P}^1$ of minimal degree $n+1$ from a general curve $C$ of genus $2 n$. Each such cover has simple ramification and its monodromy group equals $S_{n+1}$. By degenerating $C$ to a rational $g$-nodal curve, it was already known to Castelnuovo $[\mathrm{C}]$ that the number of such covers coincides with the degree of the Grassmannian $G(2, n+2)$ in its Plücker embedding, which is well-known to equal $C_n$.

# metadata.dc.publisher[].value
Centro Edizioni Scuola Normale Superiore di Pisa

# metadata.dc.relation.ispartof[].value
Annali della Scuola Normale Superiore di Pisa. Classe di Scienze, 2021, vol. XXII, num. 2, p. 665-690

# metadata.dc.rights[].value
(c) Centro Edizioni Scuola Normale Superiore di Pisa, 2021

# metadata.dc.source[].value
Articles publicats en revistes (Matemàtiques i Informàtica)

# metadata.dc.title[].value
Alternating Catalan numbers and cover with triple ramification