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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 6 |
| 3 | 42 |
| 4 | 360 |
| 5 | 3720 |
| 6 | 45360 |
| 7 | 640080 |
| 8 | 10281600 |
| 9 | 185431680 |
| 10 | 3712262400 |
| 11 | 81709689600 |
| 12 | 1961511552000 |
| 13 | 51005527372800 |
| 14 | 1428241944729600 |
| 15 | 42848566016256000 |
| 16 | 1371175035310080000 |
| 17 | 46620306887970816000 |
| 18 | 1678337450340655104000 |
| 19 | 63776944758045302784000 |
[0,1,6,42,360,3720,45360,640080,10281600, 185431680,3712262400,81709689600,1961511552000, 51005527372800,1428241944729600,42848566016256000, 1371175035310080000,46620306887970816000, 1678337450340655104000,63776944758045302784000] |