(0.5)n 

(0.5)^n
                         
0 0 7 8 1 2 5
(0.5)^7 = 0.0078125
Method: Enter 5 at B1. On B2 enter
@MOD(5*A1,10)+(5*B1-@MOD(5*B1,10))/10
              Then COPY.