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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 12 |
| 3 | 123 |
| 4 | 1234 |
| 5 | 12345 |
| 6 | 123456 |
| 7 | 1234567 |
| 8 | 12345678 |
| 9 | 123456789 |
| 10 | 12345678910 |
| 11 | 1234567891011 |
| 12 | 123456789101113 |
| 13 | 12345678910111314 |
| 14 | 1234567891011131415 |
| 15 | 123456789101113141516 |
| 16 | 12345678910111314151617 |
| 17 | 1234567891011131415161718 |
| 18 | 123456789101113141516171819 |
| 19 | 12345678910111314151617181920 |
[1,12,123,1234,12345,123456,1234567,12345678, 123456789,12345678910,1234567891011, 123456789101113,12345678910111314, 1234567891011131415,123456789101113141516, 12345678910111314151617,1234567891011131415161718, 123456789101113141516171819, 12345678910111314151617181920] |