"How Many Mathematicians Does It Take To Change A Light Bulb?" joke

None. It's left to the reader as an exercise.
None. The answer is intuitively obvious.
One. He gives it to four programmers, thereby simplifying the problem to a previous question.

How many numerical analysts does it take to change a light bulb?
3. 9967 (after six iterations).

How many mathematical logicians does it take to change a light bulb?
None. They can't do it, but they can easily prove that it can be done.

How many classical geometers does it take to change a light bulb?
None. You can't do it with a straight edge and a compass.

How many analysts does it take to change a light bulb?
Three. One to prove existence, one to prove uniqueness and one to derive a nonconstructive algorithm to do it.

How many number theorists does it take to change a light bulb?
I don't know the exact number, but I am sure it must be some rather elegant prime.