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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 23 |
| 3 | 456 |
| 4 | 7891 |
| 5 | 1234 |
| 6 | 567891 |
| 7 | 123456 |
| 8 | 78910123 |
| 9 | 456789101 |
| 10 | 2345678910 |
| 11 | 12345678910 |
| 12 | 123456789101 |
| 13 | 2345678910123 |
| 14 | 45678910123456 |
| 15 | 789101234567891 |
| 16 | 123456789101234 |
| 17 | 56789101234567891 |
| 18 | 12345678910123456 |
| 19 | 7891012345678910123 |
| 20 | 45678910123456789101 |
[1,23,456,7891,1234,567891,123456,78910123, 456789101,2345678910,12345678910,123456789101, 2345678910123,45678910123456,789101234567891, 123456789101234,56789101234567891, 12345678910123456,7891012345678910123, 45678910123456789101] |