Akm[k_,m_]:=Piecewise[{{0, (k != 3 && k != 5 && (k != 1 || m != 0)) || (m != -3 && m != 0 && m != 3)}, {A[1, 0], k == 1 && m == 0}, {-A[3, 3] + I*B[3, 3], k == 3 && m == -3}, {A[3, 0], k == 3 && m == 0}, {A[3, 3] + I*B[3, 3], k == 3 && m == 3}, {-A[5, 3] + I*B[5, 3], k == 5 && m == -3}, {A[5, 0], k == 5 && m == 0}}, A[5, 3] + I*B[5, 3]]