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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 2 |
| 3 | 8 |
| 4 | 40 |
| 5 | 240 |
| 6 | 1992 |
| 7 | 24416 |
| 8 | 483040 |
| 9 | 16343872 |
| 10 | 982635280 |
| 11 | 106979975168 |
| 12 | 21285548190080 |
| 13 | 7783083940331520 |
| 14 | 5254164116114948480 |
| 15 | 6577258363669088914432 |
| 16 | 15332656940815954900371968 |
| 17 | 66830735142688170751257497600 |
| 18 | 546722015615195079134707942219904 |
[0,2,8,40,240,1992,24416,483040,16343872, 982635280,106979975168,21285548190080, 7783083940331520,5254164116114948480, 6577258363669088914432,15332656940815954900371968, 66830735142688170751257497600, 546722015615195079134707942219904] |