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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 6 |
| 4 | 72 |
| 5 | 720 |
| 6 | 7560 |
| 7 | 90720 |
| 8 | 1270080 |
| 9 | 20381760 |
| 10 | 364694400 |
| 11 | 7125148800 |
| 12 | 150186960000 |
| 13 | 3393726336000 |
| 14 | 81882210009600 |
| 15 | 2102315389574400 |
| 16 | 57244753133568000 |
| 17 | 1647544166940672000 |
| 18 | 49957730917981286400 |
| 19 | 1591303422125646028800 |
[1,0,0,6,72,720,7560,90720,1270080,20381760, 364694400,7125148800,150186960000,3393726336000, 81882210009600,2102315389574400,57244753133568000, 1647544166940672000,49957730917981286400, 1591303422125646028800] |