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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 18 |
| 3 | 210 |
| 4 | 3696 |
| 5 | 86436 |
| 6 | 2521800 |
| 7 | 88274640 |
| 8 | 3608360064 |
| 9 | 168822613872 |
| 10 | 8901871248480 |
| 11 | 522534101560224 |
| 12 | 33804242536287744 |
| 13 | 2390169742849449216 |
| 14 | 183412961210465667072 |
| 15 | 15183107016739655860224 |
| 16 | 1348837954231568133427200 |
| 17 | 128012762381954718934183680 |
[1,3,18,210,3696,86436,2521800,88274640, 3608360064,168822613872,8901871248480, 522534101560224,33804242536287744, 2390169742849449216,183412961210465667072, 15183107016739655860224,1348837954231568133427200, 128012762381954718934183680] |