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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 6 |
| 4 | 24 |
| 5 | 60 |
| 6 | 1560 |
| 7 | 25410 |
| 8 | 242256 |
| 9 | 3508344 |
| 10 | 85882320 |
| 11 | 1724406750 |
| 12 | 32784999720 |
| 13 | 839182482996 |
| 14 | 24162605028744 |
| 15 | 659439484706730 |
| 16 | 19415319297457440 |
| 17 | 658935736181053680 |
| 18 | 23245444335085544736 |
| 19 | 835819877947421773494 |
| 20 | 32462532011236141677240 |
[1,0,0,6,24,60,1560,25410,242256,3508344,85882320, 1724406750,32784999720,839182482996, 24162605028744,659439484706730,19415319297457440, 658935736181053680,23245444335085544736, 835819877947421773494,32462532011236141677240] |