The sequence will from an A.P with
a=312=72 and a19=−4112=−832
tn=a+(n−1)d⇒t19=a+(19−1)d⇒−832=72+18d⇒d=−52a+d,a+2d+a+3d...........a+19d⇒1,−32,−4...........−39