From a show within a show.

I believe it was on "The Simpsons" (1989-present) they had a sort of "Sesame Street" parody.  And at its conclusion they gave the following credit:

"[showing this symbol: ü] This episode is brought to you by the symbol umlaut [then showing this: e] and the number e. Not the letter, but the number e, whose exponential function is the derivative of itself."