1,000,001: One to change the bulb and 1,000,000 to rebuild civilization to the point where they need light bulbs again.
At the hickory dickory dock.
One. He gives it to six Californians, thereby reducing the problem to an earlier joke...
In earlier work, Wiener  has shown that one mathematician can change a light bulb.
If k mathematicians can change a light bulb, and if one more simply watches them do it, then k+1 mathematicians will have changed the light bulb.
Therefore, by induction, for all n in the positive integers, n mathematicians can change a light bulb.
 Wiener, Matthew P., <11485@ucbvax>, Re: YALBJ, 1986