How many points would there be if you needed to draw a 21 lined mystic rose

Answer 1

If I understand the definition of a mystic rose ...

draw any circle, and place points equally spaced around the circle. Join each point to every other point.

So it becomes a question of how many lines can be drawn between any two point
For a 21 point mystic rose, that would be
C(21,2) -----> 21 choose 2
= 21!/(2!19!)
= 21(20)/2 = 210