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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 6 |
| 3 | 30 |
| 4 | 192 |
| 5 | 1560 |
| 6 | 15120 |
| 7 | 171360 |
| 8 | 2217600 |
| 9 | 32296320 |
| 10 | 522547200 |
| 11 | 9300614400 |
| 12 | 180583603200 |
| 13 | 3798482688000 |
| 14 | 86044973414400 |
| 15 | 2088355965696000 |
| 16 | 54064489070592000 |
| 17 | 1487129136869376000 |
| 18 | 43312058119249920000 |
[1,6,30,192,1560,15120,171360,2217600,32296320, 522547200,9300614400,180583603200,3798482688000, 86044973414400,2088355965696000,54064489070592000, 1487129136869376000,43312058119249920000] |