a(1) = -6 +(1-1) (1/5)
= -6+0
= -6
a(4) = -6 +(4-1)*(1/5)
= -6 +3/5
= -5 2/5
a(10) = -6 + (10-1)*1/5
= -6 +9/5
-4 1/5
