  Neutron star crust, formed via accretion of matter from a companion in a
low-mass X-ray binary (LMXB), has an equation of state (EOS) stiffer than that
of catalyzed matter. At a given neutron star mass, M, the radius of a star with
an accreted crust is therefore larger, by DR(M), than for usually considered
star built of catalyzed matter. Using a compressible liquid drop model of
nuclei, we calculate, within the one-component plasma approximation, the EOSs
corresponding to different nuclear compositions of ashes of X-ray bursts in
LMXB. These EOSs are then applied for studying the effect of different
formation scenarios on the neutron-star mass-radius relation. Assuming the SLy
EOS for neutron star's liquid core, derived by Douchin & Haensel (2001), we
find that at M=1.4 M_sun the star with accreted crust has a radius more than
100 m larger that for the crust of catalyzed matter. Using smallness of the
crust mass compared to M, we derive a formula that relates DR(M) to the
difference in the crust EOS. This very precise formula gives also analytic
dependence of DR on M and R of the reference star built of catalyzed matter.
The formula is valid for any EOS of the liquid core. Rotation of neutron star
makes DR(M) larger. We derive an approximate but very precise formula that
gives difference in equatorial radii, DR_eq(M), as a function of stellar
rotation frequency.
