I don’t mind the idea of having an * for a hole number.
There is a particular Australian course designer that builds quite poor even number holes. I felt that his best bet was to design a course that only had odd numbers. Therefore, playing 18 holes would mean starting at the 1st & ending on the 35th. If it was a 2 course complex, you could have another designer to design the even holes. Then you would have the Even course & the Odd course.
You could make a composite course out of the prime numbers.