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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 6 |
| 4 | 24 |
| 5 | 110 |
| 6 | 2760 |
| 7 | 39116 |
| 8 | 485184 |
| 9 | 10305144 |
| 10 | 238592880 |
| 11 | 5207444352 |
| 12 | 135198201600 |
| 13 | 4021267161600 |
| 14 | 122974552698816 |
| 15 | 4055791519461600 |
| 16 | 147093555900211200 |
| 17 | 5642681004581644800 |
| 18 | 228580347898812789504 |
| 19 | 9886264354137483765504 |
| 20 | 451999533867513930777600 |
[1,0,0,6,24,110,2760,39116,485184,10305144, 238592880,5207444352,135198201600,4021267161600, 122974552698816,4055791519461600, 147093555900211200,5642681004581644800, 228580347898812789504,9886264354137483765504, 451999533867513930777600] |