def METHOD_NAME(n):
    r"""Returns the :math:`n` th telephone number.
    They satisfy the recursion relation :math:`T(n) = T(n-1)+(n-1)T(n-2)` and
    :math:`T(0)=T(1)=1`.
    See https://oeis.org/A000085 for more details.
    Args:
        n (integer): index
    Returns:
        int: the nth telephone number
    """
    if n in (0, 1):
        return 1
    return METHOD_NAME(n - 1) + (n - 1) * METHOD_NAME(n - 2)