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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 2 |
| 4 | 8 |
| 5 | 39 |
| 6 | 218 |
| 7 | 1440 |
| 8 | 10922 |
| 9 | 93754 |
| 10 | 898484 |
| 11 | 9508956 |
| 12 | 110145408 |
| 13 | 1385996396 |
| 14 | 18826451052 |
| 15 | 274552411175 |
| 16 | 4278441740820 |
| 17 | 70950825535270 |
| 18 | 1247552015661833 |
| 19 | 23183674957715736 |
| 20 | 454013634588599833 |
[1,0,0,2,8,39,218,1440,10922,93754,898484,9508956, 110145408,1385996396,18826451052,274552411175, 4278441740820,70950825535270,1247552015661833, 23183674957715736,454013634588599833] |