Top rows: gravitational mass (in solar masses) versus circumferential radius of nonrotating neutron stars for the EoSs BSk19-20-21 (dots) and their analytical representations from Eq. (3) (lines). The solid and dotted parts of the lines correspond to the hydrostatically stable and unstable configurations, respectively. The dashed segment in the middle panel corresponds to superluminal EoS at the stellar center. The crosses mark the threshold beyond which the EoS becomes superluminal. The middle and bottom rows show respectively a zoom around the maximum neutron-star mass and the low mass region where the discrepancies are the largest.