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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 2 |
| 3 | 6 |
| 4 | 60 |
| 5 | 600 |
| 6 | 7680 |
| 7 | 123480 |
| 8 | 2212560 |
| 9 | 47053440 |
| 10 | 1104092640 |
| 11 | 29200802400 |
| 12 | 845985349440 |
| 13 | 26864561243520 |
| 14 | 924556913280000 |
| 15 | 34334318184566400 |
| 16 | 1367790957223891200 |
| 17 | 58194757879908249600 |
| 18 | 2633788044958380710400 |
| 19 | 126340003102675832870400 |
[1,0,2,6,60,600,7680,123480,2212560,47053440, 1104092640,29200802400,845985349440, 26864561243520,924556913280000,34334318184566400, 1367790957223891200,58194757879908249600, 2633788044958380710400,126340003102675832870400] |