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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 9 |
| 3 | 99 |
| 4 | 121 |
| 5 | 131 |
| 6 | 999 |
| 7 | 9999 |
| 8 | 12021 |
| 9 | 12121 |
| 10 | 13031 |
| 11 | 13131 |
| 12 | 99999 |
| 13 | 999999 |
| 14 | 1202021 |
| 15 | 1203021 |
| 16 | 1212121 |
| 17 | 1213121 |
| 18 | 1302031 |
| 19 | 1303031 |
| 20 | 1312131 |
| 21 | 1313131 |
| 22 | 9999999 |
| 23 | 99999999 |
| 24 | 120202021 |
| 25 | 120212021 |
| 26 | 120303021 |
| 27 | 120313021 |
| 28 | 121202121 |
| 29 | 121212121 |
[1,9,99,121,131,999,9999,12021,12121,13031,13131, 99999,999999,1202021,1203021,1212121,1213121, 1302031,1303031,1312131,1313131,9999999,99999999, 120202021,120212021,120303021,120313021,121202121, 121212121] |