> There was also the very embarrassing case of being called to the blackboard to complete a problem in an elective course on number theory only to draw a blank

> There was also the very embarrassing case of being called to the blackboard to complete a problem in an elective course on number theory only to draw a blank on what 9 times 7 was. If it's any consolation, the great mathematician Alexander Grothendieck (https://en.wikipedia.org/wiki/Alexander_Grothendieck https://en.wikipedia.org/wiki/Alexander_Grothendieck), when asked to supply a prime number (at some point in a lecture)—and being puzzled by the idea of actually naming a specific prime number—famously thought for a while before suggesting 57. (https://en.wikipedia.org/wiki/57_%28number%29#In_mathematics https://en.wikipedia.org/wiki/57_%28number%29#In_mathematics)