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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 2 |
| 3 | 16 |
| 4 | 118 |
| 5 | 926 |
| 6 | 7956 |
| 7 | 75132 |
| 8 | 777456 |
| 9 | 8771184 |
| 10 | 107307360 |
| 11 | 1416252960 |
| 12 | 20068629120 |
| 13 | 304002322560 |
| 14 | 4903642679040 |
| 15 | 83928856838400 |
| 16 | 1519397749094400 |
| 17 | 29010025797580800 |
| 18 | 582647327132774400 |
| 19 | 12280347845905305600 |
| 20 | 271030782903552000000 |
| 21 | 6251213902855219200000 |
[0,0,2,16,118,926,7956,75132,777456,8771184, 107307360,1416252960,20068629120,304002322560, 4903642679040,83928856838400,1519397749094400, 29010025797580800,582647327132774400, 12280347845905305600,271030782903552000000, 6251213902855219200000] |