Relatedly, if you ever forget Avagadro's number, you can approximate it by figuring out how many unique 5x5 bingo cards you can make by 24 words and a free space. This will get you to within about 3% of the right number.
Edit: corrected the post from 25 to 24. I got bitten by an off-by-one error in Python's range!
24! = 6.20e23; and Avogadro = 6.02e23.
Incidentally, if you're trying to explain the results of this calculation to a middle school English teacher, I recommend "More than there are grains of sand on a beach." It relaxes the worry they really have and is non-specific enough to avoid sounding threatening. (Ask me no questions I'll tell you no lies.)