Three:
One to write the light bulb removal program,
one to write the light bulb insertion program, and
one to act as a light bulb administrator to make sure nobody else tries to change the light bulb at the same time.
or
The guardians of the galaxy!
or
Twenty. One to hold the bulb, two to turn the ladder, and 17 to be on the guest list.
or
Two — one to change the bulb, and one to write a song about how good the old light bulb was.
or