| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 3 |
| 4 | 6 |
| 5 | 19 |
| 6 | 69 |
| 7 | 399 |
| 8 | 1999 |
| 9 | 9999 |
| 10 | 99999 |
| 11 | 1999999 |
| 12 | 39999999 |
| 13 | 699999999 |
| 14 | 19999999999 |
| 15 | 699999999999 |
| 16 | 39999999999999 |
| 17 | 1999999999999999 |
| 18 | 99999999999999999 |
| 19 | 9999999999999999999 |
| 20 | 1999999999999999999999 |
[0,1,3,6,19,69,399,1999,9999,99999,1999999, 39999999,699999999,19999999999,699999999999, 39999999999999,1999999999999999,99999999999999999, 9999999999999999999,1999999999999999999999] |