It's not a shrub, it's a lemon tree my dear Watson.
or
One. You don't believe me do you? I've got photos! See that big blob? Well, just squint your eyes a bit. . . .
or
One. He gives it to six Californians, thereby reducing the problem to an earlier joke...
In earlier work, Wiener [1] 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.
Bibliography:
[1] Wiener, Matthew P., <11485@ucbvax>, Re: YALBJ, 1986
or
Nearly unanswerable, since the one who tries to change it usually drops it, and the others call for a planning session.
or