| 4 |
| 5 |
| 7 |
| 52 |
| 3n−5 |
| 5n−2 |
| 3n−2 |
| 5n−1 |
则
| 1 |
| 5 |
| 1 |
| 5 |
| 4 |
| 52 |
| 7 |
| 53 |
| 3n−5 |
| 5n−1 |
| 3n−2 |
| 5n |
①-②得：
| 4 |
| 5 |
| 3 |
| 5 |
| 3 |
| 52 |
| 3 |
| 5n−1 |
| 3n−2 |
| 5n |
=1+3×
| ||||
1−
|
| 3n−2 |
| 5n |
=
| 7×5n−12n−7 |
| 4×5n |
∴Sn=
| 7×5n−12n−7 |
| 16×5n−1 |
| 4 |
| 5 |
| 7 |
| 52 |
| 3n−2 |
| 5n−1 |
| 4 |
| 5 |
| 7 |
| 52 |
| 3n−5 |
| 5n−2 |
| 3n−2 |
| 5n−1 |
| 1 |
| 5 |
| 1 |
| 5 |
| 4 |
| 52 |
| 7 |
| 53 |
| 3n−5 |
| 5n−1 |
| 3n−2 |
| 5n |
| 4 |
| 5 |
| 3 |
| 5 |
| 3 |
| 52 |
| 3 |
| 5n−1 |
| 3n−2 |
| 5n |
| ||||
1−
|
| 3n−2 |
| 5n |
| 7×5n−12n−7 |
| 4×5n |
| 7×5n−12n−7 |
| 16×5n−1 |