refer to the following pattern and answer questions

1=2^1 - 1
1+2=2^2-1
1+2+2^2=2^3-1
1+2+2^2+2^3=2^4-1
1+2+2^2+2^3+2^4=2^5-1

A. Write a simpler expression for 1+2+2^2+2