Walter Gratzer, "Eurekas and Euphoria"

During the Civil War, the future Nobel Prize winner in physics Igor Tamm was captured by one of the gangs of Makhno. He was taken to the ataman - "a bearded man in a high fur hat, whose chest met cross-crossed machine gun ribbons, and a pair of hand grenades dangled on his belt."
- You son of a bitch, communist agitator, why are you undermining Mother Ukraine? We'll kill you.
- Not at all, Tamm replied. I'm a professor at the University of Odessa and I came here to get some food.
- Bullshit! - exclaimed the ataman. - What professor are you?
- I teach mathematics.
- Mathematics? - Ataman asked. - Then find me an estimate of the MacLauren series coming in first n terms. If you decide to go free, no, I will shoot you.
Tamm could not believe his ears: the problem was a rather narrow field of higher mathematics. With trembling hands and at the barrel of a rifle, he managed to make a decision and showed it to the ataman.
- Right! said the ataman. Now I see that you are really a professor. Well, go home.
Tamm never learned the name of the ataman.