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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 0 |
| 3 | 12 |
| 4 | 104 |
| 5 | 872 |
| 6 | 8064 |
| 7 | 71680 |
| 8 | 635312 |
| 9 | 5554240 |
| 10 | 47920384 |
| 11 | 408259136 |
| 12 | 3437600192 |
| 13 | 28638307456 |
| 14 | 236298903552 |
| 15 | 1932926374400 |
| 16 | 15688543703808 |
| 17 | 126443222102016 |
| 18 | 1012619953508352 |
| 19 | 8062922404920320 |
| 20 | 63864515531578368 |
| 21 | 503439208935970816 |
[1,0,12,104,872,8064,71680,635312,5554240, 47920384,408259136,3437600192,28638307456, 236298903552,1932926374400,15688543703808, 126443222102016,1012619953508352,8062922404920320, 63864515531578368,503439208935970816] |