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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 7 |
| 3 | 50 |
| 4 | 406 |
| 5 | 3804 |
| 6 | 41028 |
| 7 | 506064 |
| 8 | 7084656 |
| 9 | 111690720 |
| 10 | 1967421600 |
| 11 | 38425449600 |
| 12 | 825970435200 |
| 13 | 19404363283200 |
| 14 | 495012834489600 |
| 15 | 13632039812966400 |
| 16 | 403120633444300800 |
| 17 | 12740557701389414400 |
| 18 | 428546132879432601600 |
| 19 | 15284163618598275072000 |
| 20 | 576073025410937628672000 |
[0,1,7,50,406,3804,41028,506064,7084656,111690720, 1967421600,38425449600,825970435200, 19404363283200,495012834489600,13632039812966400, 403120633444300800,12740557701389414400, 428546132879432601600,15284163618598275072000, 576073025410937628672000] |