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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 12 |
| 3 | 123 |
| 4 | 1234 |
| 5 | 12346 |
| 6 | 123467 |
| 7 | 1234678 |
| 8 | 12346789 |
| 9 | 1234678910 |
| 10 | 123467891011 |
| 11 | 12346789101112 |
| 12 | 1234678910111213 |
| 13 | 123467891011121314 |
| 14 | 12346789101112131415 |
| 15 | 1234678910111213141516 |
| 16 | 123467891011121314151617 |
| 17 | 12346789101112131415161718 |
| 18 | 1234678910111213141516171819 |
| 19 | 123467891011121314151617181920 |
[1,12,123,1234,12346,123467,1234678,12346789, 1234678910,123467891011,12346789101112, 1234678910111213,123467891011121314, 12346789101112131415,1234678910111213141516, 123467891011121314151617, 12346789101112131415161718, 1234678910111213141516171819, 123467891011121314151617181920] |