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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 1 |
| 4 | 4 |
| 5 | 24 |
| 6 | 138 |
| 7 | 1032 |
| 8 | 8160 |
| 9 | 75600 |
| 10 | 751680 |
| 11 | 8436960 |
| 12 | 100679040 |
| 13 | 1327052160 |
| 14 | 18525024000 |
| 15 | 280451808000 |
| 16 | 4477627123200 |
| 17 | 76690072166400 |
| 18 | 1377634946688000 |
| 19 | 26328977260185600 |
| 20 | 525869478021888000 |
| 21 | 11092929741653760000 |
| 22 | 243781091314016256000 |
| 23 | 5628622656645660672000 |
[1,0,0,1,4,24,138,1032,8160,75600,751680,8436960, 100679040,1327052160,18525024000,280451808000, 4477627123200,76690072166400,1377634946688000, 26328977260185600,525869478021888000, 11092929741653760000,243781091314016256000, 5628622656645660672000] |