Stanley Weinbaum 
Brink of Infinity [EPUB ebook] 

A math professor, thinking that he has been hired by a chemist to run some statistical analyses on experimental data, is surprised to learn that is the experiment. The chemist, angry at mathematicians because a miscalculation by one resulted in him being crippled in an explosion, wishes to separate the mathematicians from the bogus ones who – in his opinion – deserve to die. To test whether the protagonist is a real mathematician, he must guess the mathematical expression that the kidnapper is thinking of by asking ten questions…