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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 3 |
| 5 | 9 |
| 6 | 48 |
| 7 | 131 |
| 8 | 334 |
| 9 | 880 |
| 10 | 2355 |
| 11 | 6341 |
| 12 | 17157 |
| 13 | 47620 |
| 14 | 132015 |
| 15 | 366790 |
| 16 | 1025835 |
| 17 | 2884928 |
| 18 | 8143498 |
[0,0,0,3,9,48,131,334,880,2355,6341,17157,47620, 132015,366790,1025835,2884928,8143498] |