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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 24 |
| 4 | 240 |
| 5 | 3120 |
| 6 | 54720 |
| 7 | 1169280 |
| 8 | 30804480 |
| 9 | 950745600 |
| 10 | 34459084800 |
| 11 | 1424870092800 |
| 12 | 67133032243200 |
| 13 | 3540086232883200 |
| 14 | 208397961547776000 |
| 15 | 13533822947893248000 |
| 16 | 966773828738285568000 |
| 17 | 75334352557782269952000 |
| 18 | 6385175803136642383872000 |
[1,1,4,24,240,3120,54720,1169280,30804480, 950745600,34459084800,1424870092800, 67133032243200,3540086232883200, 208397961547776000,13533822947893248000, 966773828738285568000,75334352557782269952000, 6385175803136642383872000] |