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| n | a(n) |
|---|---|
| 0 | 0 |
| 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 |
| 19 | 909090909090909091 |
| 20 | 9090909090909090909 |
| 21 | 90909090909090909091 |
[0,1,9,91,909,9091,90909,909091,9090909,90909091, 909090909,9090909091,90909090909,909090909091, 9090909090909,90909090909091,909090909090909, 9090909090909091,90909090909090909, 909090909090909091,9090909090909090909, 90909090909090909091] |