In my copious spare time, I occasionally amuse myself by doing some physics problems (out of this book). Sometimes a problem expresses a time in years, and since it’s usually a good idea to convert times into seconds, one sometimes has to figure out how many seconds there are in a (365-day) year. Fortunately, someone with a good knowledge of Broadway musicals can save some steps by just noting that the answer is 525,600 x 60.
UPDATE: Commenter Eric Jablow points out that xkcd did this already.