def METHOD_NAME(gate_indices, number_of_qubits):
    """Return the index string for Numpy.einsum matrix-vector multiplication.
    The returned indices are to perform a matrix multiplication A.v where
    the matrix A is an M-qubit matrix, vector v is an N-qubit vector, and
    M <= N, and identity matrices are implied on the subsystems where A has no
    support on v.
    Args:
        gate_indices (list[int]): the indices of the right matrix subsystems
                                  to contract with the left matrix.
        number_of_qubits (int): the total number of qubits for the right matrix.
    Returns:
        str: An indices string for the Numpy.einsum function.
    """
    mat_l, mat_r, tens_lin, tens_lout = _einsum_matmul_index_helper(gate_indices, number_of_qubits)
    # Combine indices into matrix multiplication string format
    # for numpy.einsum function
    return f"{mat_l}{mat_r}, " + "{tens_lin}->{tens_lout}".format(
        tens_lin=tens_lin, tens_lout=tens_lout
    )