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
Three, One to climb the ladder. One to shake it. And one to sue the ladder company.
or
Two — one to screw it most of the way in and the other to give it a surprise twist at the end.
or