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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 2 |
| 3 | 6 |
| 4 | 58 |
| 5 | 460 |
| 6 | 5528 |
| 7 | 70308 |
| 8 | 1098060 |
| 9 | 18910512 |
| 10 | 371480832 |
| 11 | 8022952080 |
| 12 | 191325228576 |
| 13 | 4961955705408 |
| 14 | 139572074260656 |
| 15 | 4224646630879920 |
| 16 | 137077496211066384 |
| 17 | 4744151145076980864 |
| 18 | 174517898073769832448 |
| 19 | 6798949897214608689024 |
| 20 | 279688643858492900930496 |
[1,0,2,6,58,460,5528,70308,1098060,18910512, 371480832,8022952080,191325228576,4961955705408, 139572074260656,4224646630879920, 137077496211066384,4744151145076980864, 174517898073769832448,6798949897214608689024, 279688643858492900930496] |