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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | -9 |
| 3 | 91 |
| 4 | -909 |
| 5 | 9091 |
| 6 | -90909 |
| 7 | 909091 |
| 8 | -9090909 |
| 9 | 90909091 |
| 10 | -909090909 |
| 11 | 9090909091 |
| 12 | -90909090909 |
| 13 | 909090909091 |
| 14 | -9090909090909 |
| 15 | 90909090909091 |
| 16 | -909090909090909 |
| 17 | 9090909090909091 |
| 18 | -90909090909090909 |
[1,-9,91,-909,9091,-90909,909091,-9090909, 90909091,-909090909,9090909091,-90909090909, 909090909091,-9090909090909,90909090909091, -909090909090909,9090909090909091, -90909090909090909] |