I’m a big fan of Sporcle, a website that has, as they describe it, “mentally stimulating diversions.”
When I was in graduate school, one of my fellow graduate students had a terrible time learning the Greek letters. He forgot the easy ones—he repeatedly called lambda, gamma and phi, psi. His advisor joked (I think he was joking) that he wouldn’t allow my friend to get his PhD until he learned the Greek alphabet. Well, here’s the Sporcle game for him:
According the the stats page for the game, 31% of the players were able to get all the letters correct in 5 minutes and the most missed letter is 
For other math-related games at Sporcle, try:
By the way, my friend did earn a PhD!
David Richeson: Division by Zero 