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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 14 |
| 3 | 78 |
| 4 | 504 |
| 5 | 3720 |
| 6 | 30960 |
| 7 | 287280 |
| 8 | 2943360 |
| 9 | 33022080 |
| 10 | 402796800 |
| 11 | 5308934400 |
| 12 | 75203251200 |
| 13 | 1139544806400 |
| 14 | 18394619443200 |
| 15 | 315149522688000 |
| 16 | 5711921639424000 |
| 17 | 109196040425472000 |
| 18 | 2196014181064704000 |
| 19 | 46346783255764992000 |
| 20 | 1024251745442365440000 |
[1,3,14,78,504,3720,30960,287280,2943360,33022080, 402796800,5308934400,75203251200,1139544806400, 18394619443200,315149522688000,5711921639424000, 109196040425472000,2196014181064704000, 46346783255764992000,1024251745442365440000] |