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| n | a(n) |
|---|---|
| 0 | 2 |
| 1 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 6 |
| 5 | 30 |
| 6 | 180 |
| 7 | 1440 |
| 8 | 12960 |
| 9 | 142560 |
| 10 | 1995840 |
| 11 | 29937600 |
| 12 | 538876800 |
| 13 | 10777536000 |
| 14 | 226328256000 |
| 15 | 5205549888000 |
| 16 | 135344297088000 |
| 17 | 3924984615552000 |
| 18 | 117749538466560000 |
| 19 | 3885734769396480000 |
| 20 | 136000716928876800000 |
| 21 | 4896025809439564800000 |
| 22 | 190945006568143027200000 |
[2,1,1,2,6,30,180,1440,12960,142560,1995840, 29937600,538876800,10777536000,226328256000, 5205549888000,135344297088000,3924984615552000, 117749538466560000,3885734769396480000, 136000716928876800000,4896025809439564800000, 190945006568143027200000] |