  The one-neutron halos lying in the island of inversion around $N=20$ has
provided the podium, to study the variation of total low-lying dipole strength
with the neutron separation energy. We study three probable p-wave one-neutron
halo candidates 31Ne and 34Na and 37Mg lying in the island of inversion. A
simple analytic model has been used for the calculation of the total low-lying
dipole strength for the medium mass p-wave one-neutron halos. A correction
factor to this analytical model has been estimated with a realistic Woods-Saxon
potential. A comparison of these analytic calculations has been made with the
those performed by a finite-range distorted-wave Born approximation theory of
the Coulomb dissociation. We also make an estimate of the one-neutron
separation energies of 31Ne, 34Na and 37Mg.
