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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 3 |
| 3 | 33 |
| 4 | 55 |
| 5 | 555 |
| 6 | 777 |
| 7 | 7777 |
| 8 | 9999 |
| 9 | 99999 |
| 10 | 1111111111 |
| 11 | 111111111111 |
| 12 | 131313131313 |
| 13 | 13131313131313 |
| 14 | 15151515151515 |
| 15 | 1515151515151515 |
| 16 | 1717171717171717 |
| 17 | 171717171717171717 |
| 18 | 191919191919191919 |
| 19 | 19191919191919191919 |
| 20 | 21212121212121212121 |
| 21 | 2121212121212121212121 |
[1,3,33,55,555,777,7777,9999,99999,1111111111, 111111111111,131313131313,13131313131313, 15151515151515,1515151515151515,1717171717171717, 171717171717171717,191919191919191919, 19191919191919191919,21212121212121212121, 2121212121212121212121] |