Laurel sent me this gem1, which lead me to find the wikipedia page on Mathematical Jokes:

A Dozen, a Gross, and a Score,

plus three times the square root of four,

divided by seven,

plus five times eleven,

equals nine squared and not a bit more.

And from there, I found another:

Integral z-squared dz

From 1 to the cube root of 3

Times the cosine

Of three pi over 9

Equals log of the cube root of e.

Apparently by Leigh Mercer ↩