Megagon

Find the constant of proportionality for a decagon, kilogon, and megagon.

There can exist a regular polygon with 1000 sides (this might be called a "regular kilogon"), 1,000,000 sides (a "regular megagon"), or 1,000,000,000 sides (a "regular gigagon").

A megagon is close to the perfection of a circle — a kind of generational transmutation.