7
votes
2answers
284 views

What is the number of noncrossing acyclic digraphs?

A noncrossing graph on $n$ vertices is a graph drawn on $n$ points numbered from $1$ to $n$ in counter-clockwise order on a circle such that the edges lie entirely within the circle and do not cross ...
0
votes
2answers
252 views

Enumeration Result [closed]

Hi I have a very soft question: What exactly is the definition of an enumeration result? Let say I want to enumerate some combinatorial structure and I came up with an equation for a generating ...
20
votes
1answer
741 views

A strange sum over bipartite graphs

While mucking around with some generating functions related to enumeration of regular bipartite graphs, I stumbled across the following cutie. I wonder if anyone has seen it before, and/or if anyone ...