Akm[k_,m_]:=Piecewise[{{0, k != 3 || (m != -2 && m != 0 && m != 2)}, {A[3, 2] - I*B[3, 2], k == 3 && m == -2}, {A[3, 0], k == 3 && m == 0}}, A[3, 2] + I*B[3, 2]]