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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 0 |
| 5 | 0 |
| 6 | 0 |
| 7 | 1 |
| 8 | 5 |
| 9 | 35 |
| 10 | 179 |
| 11 | 909 |
| 12 | 4285 |
| 13 | 19702 |
| 14 | 88040 |
| 15 | 386826 |
| 16 | 1674852 |
| 17 | 7174436 |
| 18 | 30462009 |
[0,0,0,0,0,0,1,5,35,179,909,4285,19702,88040, 386826,1674852,7174436,30462009] |