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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 44 |
| 3 | 792 |
| 4 | 19800 |
| 5 | 633600 |
| 6 | 24710400 |
| 7 | 1136678400 |
| 8 | 60243955200 |
| 9 | 3614637312000 |
| 10 | 242180699904000 |
| 11 | 17921371792896000 |
| 12 | 1451631115224576000 |
| 13 | 127743538139762688000 |
| 14 | 12135636123277455360000 |
| 15 | 1237834884574300446720000 |
| 16 | 134924002418598748692480000 |
| 17 | 15651184280557454848327680000 |
[1,4,44,792,19800,633600,24710400,1136678400, 60243955200,3614637312000,242180699904000, 17921371792896000,1451631115224576000, 127743538139762688000,12135636123277455360000, 1237834884574300446720000, 134924002418598748692480000, 15651184280557454848327680000] |