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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 0 |
| 5 | 1 |
| 6 | 1 |
| 7 | 2 |
| 8 | 5 |
| 9 | 12 |
| 10 | 40 |
| 11 | 154 |
| 12 | 766 |
| 13 | 4672 |
| 14 | 34547 |
| 15 | 302185 |
| 16 | 3073267 |
| 17 | 35933851 |
| 18 | 479768761 |
| 19 | 7284446498 |
| 20 | 125435333136 |
[0,0,0,0,1,1,2,5,12,40,154,766,4672,34547,302185, 3073267,35933851,479768761,7284446498, 125435333136] |