2 |
3 |
1 |
an-1 |
1 |
an+1 |
2 |
an |
1 |
an |
1 |
a2 |
1 |
a1 |
1 |
2 |
1 |
an |
1 |
2 |
2 |
n+1 |
4 |
(n+1)(n+2) |
1 |
n+1 |
1 |
n+2 |
1 |
2 |
1 |
3 |
1 |
3 |
1 |
4 |
1 |
n+1 |
1 |
n+2 |
1 |
2 |
1 |
n+2 |
2n |
n+2 |
4 |
(n+1)2 |
4 |
n(n+1) |
1 |
n+1 |
1 |
n+2 |
1 |
2 |
1 |
2 |
1 |
3 |
1 |
n+1 |
1 |
n+2 |
1 |
n+1 |
n+1 |
n+2 |
5 |
6 |
S2n |
Sn |
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