Let be a circle passing through the points , , and .
For positive integers and , let be a configuration which consists of the circles: .
An Eulerian cycle on is a closed path that passes through each arc exactly once.
Many such paths are possible on , but we are only interested in those which are not self-crossing: a non-crossing path just touches itself at lattice points, but it never crosses itself.
The image below shows and an example of an Eulerian non-crossing path.
Let be the number of Eulerian non-crossing paths on .
For example, , and .
Find .
Write-up coming later
The complete problem is available here. An approach, code, and answer will be added later.