Data:8 7/HOMFLYPT Polynomial

${\frac {z^{6}}{a^{2}}}+{\frac {5z^{4}}{a^{2}}}-{\frac {z^{4}}{a^{4}}}-z^{4}+{\frac {8z^{2}}{a^{2}}}-{\frac {3z^{2}}{a^{4}}}-3z^{2}+{\frac {4}{a^{2}}}-{\frac {2}{a^{4}}}-1$