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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 0 |
| 5 | 120 |
| 6 | 1080 |
| 7 | 8820 |
| 8 | 75600 |
| 9 | 701568 |
| 10 | 25235280 |
| 11 | 736589040 |
| 12 | 17454333600 |
| 13 | 376218063936 |
| 14 | 7825958011872 |
| 15 | 207779505635520 |
| 16 | 7160585771888640 |
| 17 | 266170809822432768 |
| 18 | 9680346223607877120 |
| 19 | 339097779148341335040 |
| 20 | 12234333214554427699200 |
| 21 | 488121623700513688166400 |
[1,0,0,0,0,120,1080,8820,75600,701568,25235280, 736589040,17454333600,376218063936,7825958011872, 207779505635520,7160585771888640, 266170809822432768,9680346223607877120, 339097779148341335040,12234333214554427699200, 488121623700513688166400] |