25．已知数列{an}\{a_{n}\}{an}满足an=2an−1(n⩾2,n∈N∗)a_{n}=2a_{n-1}(n\geqslant 2,n\in N^{*})an=2an−1(n⩾2,n∈N∗)，且a1=1a_{1}=1a1=1，则an=a_{n}=an=___2n−12^{n-1}2n−1[，]n∈N∗n\in N^{*}n∈N∗___．