Akm[k_,m_]:=Piecewise[{{A[0, 0], k == 0 && m == 0}, {A[1, 0], k == 1 && m == 0}, {A[2, 0], k == 2 && m == 0}, {A[3, 0], k == 3 && m == 0}, {A[4, 4] - I*B[4, 4], k == 4 && m == -4}, {A[4, 0], k == 4 && m == 0}, {A[4, 4] + I*B[4, 4], k == 4 && m == 4}, {A[5, 4] - I*B[5, 4], k == 5 && m == -4}, {A[5, 0], k == 5 && m == 0}, {A[5, 4] + I*B[5, 4], k == 5 && m == 4}, {A[6, 4] - I*B[6, 4], k == 6 && m == -4}, {A[6, 0], k == 6 && m == 0}, {A[6, 4] + I*B[6, 4], k == 6 && m == 4}}, 0]