A (n+1)-= 2 n
An-A (n-1) = 2 (n-1)
an-a(n- 1)=2^(n- 1)( 1)
a(n- 1)-a(n-2)=2^(n-2) (2)
...
a2 -a 1 = 2^0 (n- 1)
( 1)+(2)+...+(n- 1)
an -a 1 = 2^0+2^ 1+....+2^(n- 1)
= 2^(n- 1) - 1
An-1= 2 (n-1)-1
An = 2 (n-1)