1 |
a1 |
1 |
a2 |
1 |
an |
n(n+1) |
2 |
1 |
an |
2 |
n(n+1) |
1 |
n |
1 |
n+1 |
1 |
a1 |
1 |
a2 |
1 |
an |
1 |
2 |
1 |
2 |
1 |
3 |
1 |
n |
1 |
n+1 |
1 |
n+1 |
2n |
n+1 |
2n |
n+1 |
A.40 | B.35 | C.30 | D.28 |
A.-2 | B.2 | C.0 | D.不确定 |
A.6 | B.9 | C.12 | D.24 |
an+an+2 |
2 |
OB |
OA |
OC |
A.2009 | B.
| C.22009 | D.2-2009 |
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