∴(an+1-an)=2(an-an-1)(n≥2)
∵a1=2,a2=4∴a2-a1=2≠0,∴an+1-an≠0
故數(shù)列{an+1-an}是公比為2的等比數(shù)列
∴an+1-an=(a2-a1)2n-1=2n
∴an=(an-an-1)+(an-1-an-2)+(an-2-an-3)++(a2-a1)+a1
=2n-1+2n-2+2n-3++21+2
=
2(1?2n?1) |
1?2 |
又a1=2滿足上式,
∴an=2n(n∈N*)
(II)由(I)知bn=
2(an?1) |
an |
1 |
an |
1 |
2n |
1 |
2n?1 |
∴Sn=2n?(1+
1 |
21 |
1 |
22 |
1 |
2n?1 |
=2n?
1?
| ||
1?
|
=2n?2(1?
1 |
2n |
=2n?2+
1 |
2n?1 |
由Sn>2010得:2n?2+
1 |
2n?1 |
即n+
1 |
2n |