The Feeling of Power
Whether this story has sufficient robot content in it to merit a place on this page is debatable, except that Asimov himself included it in the collection Robot Dreams. It's also one of my favourite stories, so I'm reviewing it anyway.
This story is about a computer programmer of the future who discovers that computers are not the only ones able to do mathematics. The story starts of quite humorously, as you realize just how little every knows about how their own creations (the computers) work. Then the story starts getting nasty: a military man suggests that humans should be required to expend themselves in war instead of computers, because they are less valuable. The story ends with the original programmer discovering the enormous horror of what he has discovered, and not being able to cope.
'"Yes, I Know," said the Technician earnestly, "but I start by saying seven times three because that's the way it works. Now seven times three is twenty-one."
"And how do you know that?" asked the congressman.
"I just remember it. It's always twenty-one on the computer. I've checked it any number of times."
"That doesn't means it always will be though, does it?" asked the congressman.'