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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 4 |
| 3 | 12 |
| 4 | 96 |
| 5 | 760 |
| 6 | 7260 |
| 7 | 80724 |
| 8 | 1008112 |
| 9 | 14079888 |
| 10 | 216881460 |
| 11 | 3652767580 |
| 12 | 66773963784 |
| 13 | 1316433381432 |
| 14 | 27840054610732 |
| 15 | 628626642921060 |
| 16 | 15093709672205280 |
| 17 | 383989133237230624 |
| 18 | 10317497504580922212 |
| 19 | 291958800400148127660 |
| 20 | 8678485827979443326200 |
[1,0,4,12,96,760,7260,80724,1008112,14079888, 216881460,3652767580,66773963784,1316433381432, 27840054610732,628626642921060,15093709672205280, 383989133237230624,10317497504580922212, 291958800400148127660,8678485827979443326200] |