For this you need to note that "n" represents position of sequence.
y1 is y on position 1 and so on. Sequence goes: y1,y2,y3,y4... and so on
So all you have to do is to implement values 1,2,3,4,5 for n and get 5 members of sequence. (start from 0 if your n starts from 0)
y0 = -5
y1 = -5-5 = -10
y2 = -15
y3 = -20
y4 = -25
y5 = -5*5 - 5 = -30
