Why is l=3 for the orbital angular momentum of a hydrogen 6f state?

[Linus Pauling]

I was asked for the energy and orbital angular momentum of a hydrogen atom in the 6f state. Thus, with n = 6 I found E to be -0.378, a straightforward calculation.

I am confused about L, though. L = sqrt[l(l+1)]. Since n = 6, I thought l = n-1, so L would be sqrt(30)*h-bar, but the answer is sqrt(12)*h-bar, so l must be 3. Why?

 

[vela]

The quantum number l can range from 0 to n-1, so the fact that n=6 only tells you l could be any integer from 0 to 5. What does the "f" stand for in "6f"?