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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 3 |
| 4 | 6 |
| 5 | 20 |
| 6 | 540 |
| 7 | 4284 |
| 8 | 35700 |
| 9 | 698760 |
| 10 | 10591560 |
| 11 | 155024100 |
| 12 | 3231336240 |
| 13 | 68704908480 |
| 14 | 1451024062488 |
| 15 | 35843008924800 |
| 16 | 950925111973200 |
| 17 | 25881184257364800 |
| 18 | 765471782499860160 |
| 19 | 24210772652940214320 |
| 20 | 797021694060934204800 |
| 21 | 27752674398657594805440 |
[1,0,0,3,6,20,540,4284,35700,698760,10591560, 155024100,3231336240,68704908480,1451024062488, 35843008924800,950925111973200,25881184257364800, 765471782499860160,24210772652940214320, 797021694060934204800,27752674398657594805440] |