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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 24 |
| 5 | 152 |
| 6 | 1072 |
| 7 | 8512 |
| 8 | 71680 |
| 9 | 662080 |
| 10 | 6603392 |
| 11 | 71748864 |
| 12 | 837838848 |
| 13 | 10499561984 |
| 14 | 139880866816 |
| 15 | 1976422924288 |
| 16 | 29453086916608 |
| 17 | 462014697656320 |
| 18 | 7601785735454720 |
| 19 | 130960983301496832 |
| 20 | 2356171689814425600 |
| 21 | 44197586399696322560 |
| 22 | 862635671043302490112 |
[0,1,2,6,24,152,1072,8512,71680,662080,6603392, 71748864,837838848,10499561984,139880866816, 1976422924288,29453086916608,462014697656320, 7601785735454720,130960983301496832, 2356171689814425600,44197586399696322560, 862635671043302490112] |