None, but it takes at least one to sit and pray for the old one to go back on.
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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
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Two. One to take out the bulb and drop it, and the other to try and sell it before it crashes (knowing that it's already burned out).
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Fifty — one to screw in the bulb and 49 to guard him/her.
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Greece!
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