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| n | a(n) |
|---|---|
| 0 | 3 |
| 1 | 0 |
| 2 | 3 |
| 3 | 1 |
| 4 | 9 |
| 5 | 6 |
| 6 | 45 |
| 7 | 42 |
| 8 | 279 |
| 9 | 320 |
| 10 | 1977 |
| 11 | 2610 |
| 12 | 15306 |
| 13 | 22404 |
| 14 | 126300 |
| 15 | 200158 |
| 16 | 1093515 |
| 17 | 1846314 |
| 18 | 9830547 |
| 19 | 17481864 |
[3,0,3,1,9,6,45,42,279,320,1977,2610,15306,22404, 126300,200158,1093515,1846314,9830547,17481864] |