[seqfan] What was Euler's original notation for the totient function?

[Alonso Del Arte]

I read somewhere that at first Euler notated his famous totient function as
pi(n) rather than phi(n). But now I can't remember what that book was. Maybe
it was a biography of Euler, but I haven't read many biographies from
beginning to end. Anyway, I would appreciate any book that says what Euler's
original notation was.

Al