User:Jim Snyder-Grant

Who is this?

Jim Snyder-Grant, independent researcher in Acton, MA, USA

Research Interest for OEIS

I've been investigating unlabelled directed graphs with a single sink, with or without self-loops allowed.

For OEIS I'd like to add some sequences related to enumerating this type of digraph.

Enumerating unlabelled digraphs of this type is a hard-ish problem. I've been able to generate the first few entries For the self-loops allowed version, the first few entries starting with 1 vertex is 1, 2, 18, 440, 32404, 7423456, 5473328160

For no self-loops allowed, the first few entries are 1, 1, 5, 60, 2126, 236560, 86140208

This seems worth pursuing because neither of these sequences is currently in the OEIS.

Update Dec 15, 2021: Added C code to generate graphs and count them: [1]

Update Dec 28, 2021: Entry for the no-loops version [2] was accepted after helpful suggestions from Andrew Howroyd [3].

Eighteen directed graphs of order 3 with a single sink, self-loops allowed

, , , , , , , , , , , , , , , , ,

(The labels shown can be ignored: they are just the canonical labellings created by the generating procedure. Label '0' is always the single sink).