About 12 weeks ago, there were 21 mold spores found in a garden. After a few weeks of observation, it is determined that the number of mold spores in the garden is tripling every 6 weeks. The number of mold spores, M, at any given time in the garden is equal to the product of the initial amount of spores, I, and 3 to the power of n, where n is the number of times the amount of mold spores has tripled. How many mold spores are in the garden today?