def brunet_w(num_types, num_tokens):
    """Calculate Brunet’s W (1978).

    Used formula:
        .. math::
            W = V^{V^{0.172}}

    Parameters:
        num_types (int): Absolute number of types.
        num_tokens (int): Absolute number of tokens.
    """
    a = -0.172
    return num_tokens ** num_types ** -a
