The examples of parallelogram are showed as below:
How to get the amount of ALL the parallelogram by GH?
Untitled.dxf (173.5 KB)
You mean the number of all possible parallelograms?
Yes, exactly.
Hello,
Nice challenge 
no immediate ideas about how to do this with Grasshopper but why do you ask - what underlying problem are you trying to solve and why? Are you looking for a general solution for any regular triangular mesh with all identical triangles inside?
maybe something related:
Edit. just saw the author is the same, so probably related