  The weight hierarchy of one-point algebraic geometry codes can be estimated
by means of the generalized order bounds, which are described in terms of a
certain Weierstrass semigroup. The asymptotical behaviour of such bounds for r
> 1 differs from that of the classical Feng-Rao distance (r=1) by the so-called
Feng-Rao numbers. This paper is addressed to compute the Feng-Rao numbers for
numerical semigroups of embedding dimension two (with two generators),
obtaining a closed simple formula for the general case by using numerical
semigroup techniques. These involve the computation of the Ap\'ery set with
respect to an integer of the semigroups under consideration. The formula
obtained is applied to lower-bounding the generalized Hamming weights,
improving the bound given by Kirfel and Pellikaan in terms of the classical
Feng-Rao distance. We also compare our bound with a modification of the
Griesmer bound, improving this one in many cases.
