2^100 - (2^99 + 2^98 + .+ 2^2 + 2)
= 2^100 - A
A = 2^99 + 2^98 + .+ 2^2 + 2 ----------------(1)
2A = 2^100 + 2^99 + 2^98 + .+ 2^3 + 4 -------(2)
(2) - (1)
A = 2^100 - 2
所以原式 ＝ 2