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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 6 |
| 2 | 48 |
| 3 | 342 |
| 4 | 2400 |
| 5 | 16806 |
| 6 | 117648 |
| 7 | 823542 |
| 8 | 5764800 |
| 9 | 40353606 |
| 10 | 282475248 |
| 11 | 1977326742 |
| 12 | 13841287200 |
| 13 | 96889010406 |
| 14 | 678223072848 |
| 15 | 4747561509942 |
| 16 | 33232930569600 |
| 17 | 232630513987206 |
| 18 | 1628413597910448 |
| 19 | 11398895185373142 |
[0,6,48,342,2400,16806,117648,823542,5764800, 40353606,282475248,1977326742,13841287200, 96889010406,678223072848,4747561509942, 33232930569600,232630513987206,1628413597910448, 11398895185373142] |