| 1 |
| 1+2+…+(n+1) |
| 1 | ||
|
=
| 2 |
| (n+1)(n+2) |
| 1 |
| n+1 |
| 1 |
| n+2 |
∴数列
| 1 |
| 1+2 |
| 1 |
| 1+2+3 |
| 1 |
| 1+2+…+(n+1) |
Sn=2（
| 1 |
| 2 |
| 1 |
| 3 |
| 1 |
| 3 |
| 1 |
| 4 |
| 1 |
| n+1 |
| 1 |
| n+2 |
=2（
| 1 |
| 2 |
| 1 |
| n+2 |
=
| n |
| n+2 |
| 1 |
| 1+2 |
| 1 |
| 1+2+3 |
| 1 |
| 1+2+…+(n+1) |
| 1 |
| 1+2+…+(n+1) |
| 1 | ||
|
| 2 |
| (n+1)(n+2) |
| 1 |
| n+1 |
| 1 |
| n+2 |
| 1 |
| 1+2 |
| 1 |
| 1+2+3 |
| 1 |
| 1+2+…+(n+1) |
| 1 |
| 2 |
| 1 |
| 3 |
| 1 |
| 3 |
| 1 |
| 4 |
| 1 |
| n+1 |
| 1 |
| n+2 |
| 1 |
| 2 |
| 1 |
| n+2 |
| n |
| n+2 |