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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 8 |
| 4 | 48 |
| 5 | 120 |
| 6 | 2640 |
| 7 | 30240 |
| 8 | 201600 |
| 9 | 4838400 |
| 10 | 96163200 |
| 11 | 1037836800 |
| 12 | 30496435200 |
| 13 | 828193766400 |
| 14 | 13686991718400 |
| 15 | 450537408921600 |
| 16 | 15880397524992000 |
| 17 | 356398802952192000 |
| 18 | 13410127414075392000 |
| 19 | 569542360114151424000 |
| 20 | 16614774394239909888000 |
[1,1,8,48,120,2640,30240,201600,4838400,96163200, 1037836800,30496435200,828193766400, 13686991718400,450537408921600,15880397524992000, 356398802952192000,13410127414075392000, 569542360114151424000,16614774394239909888000] |