The number of orbitals in a shell is the square of the principal quantum number: 12 = 1, 22 = 4, 32 = 9.
There is one orbital in an s subshell (l = 0), three orbitals in a p subshell (l = 1), and five orbitals in a d subshell (l = 2). The number of orbitals in a subshell is therefore 2(l) + 1.
